I’ll put it this way: just because the lights are on doesn’t mean anyone’s home.
You turn on your computer. It makes noise. You can see lights — perhaps even blinking lights — and assume it must be running.
It might be.
The problem is, it might not be running at all.
Become a Patron of Ask Leo! and go ad-free!
- Blinking lights and running fans mean there’s power, but little else.
- Beeps and the power-on self test (POST) can provide useful information, though beep information is BIOS-specific.
- No beeps at all often mean a fundamental hardware problem relating to the CPU, motherboard, other components, or even the power supply.
- A broken or disconnected monitor can make it appear as though the computer is broken.
Lights and noise mean very little
The phrase “everything inside it runs” is impossible to prove just by looking.
You hear the fans all start to blow, disks might start to spin, and you might see some lights come on, but all that tells you is the computer has power.
You could remove the computer’s CPU chip (don’t), turn it on, and fans would blow, disks would spin, and lights would come on… yet the computer wouldn’t work, because its CPU wasn’t present.
All you really know at this point is that the computer has power, which is good. The bad news is, you can’t assume much more.
Did it beep?
One of the more underrated and useful diagnostic tools for problems of this sort is the beep. That beep is generated by software — specifically, the UEFI or BIOS installed in your computer.
If you hear the beep, the CPU is working, the BIOS seems intact, and at least some RAM is working.
One beep is typical, and indicates things are well, at least to a point. If you hear more than one beep — if it sounds like your computer is beeping out Morse code1 — it’s trying to tell you something. It’s trying to tell you something isn’t working, and may even be trying to tell you what isn’t working.
The POST (or Power On Self Test) has detected a problem, and is using a pattern of beeps to tell you something is wrong. Unfortunately, what beep codes mean depends on the BIOS manufacturer. There’s a fairly comprehensive list here.
Why beeps? The BIOS can’t assuming anything is working, including the display. With no way to show you the problem, beep codes are its way to talk to the outside world.
No beeps?
If you don’t hear any beep at all, it’s likely you have a more serious problem2.
One or more of the CPU, RAM, motherboard, or some other hardware component isn’t working.
Exactly what has failed is not something you’ll be able to tell from the outside. You’ll probably need to find a technician to have a look.
One beep, but no display?
If the computer gives you one “all is well” beep when it starts up and you still don’t see anything on the monitor, then it’s time for a very fundamental test of your own.
Check the monitor. More specifically, check that it’s turned on, connected, and the connections are good.
If you still don’t have display, this is a great time to borrow a monitor and connect it as an external monitor to your laptop, or temporarily swap out your desktop monitor. Borrow a cable, too; they can and do fail. If the borrowed equipment works, then you know it’s your monitor or cable needing repair or replacement, not your computer.
If the borrowed equipment doesn’t work, that points back to the computer itself as the source of trouble. Anything, from CPU, RAM, and video problems to the power supply, could be at fault.
Sometimes, you just need a technician
Just like sometimes you need a mechanic to repair your car, sometimes you need a technician to diagnose your computer.
Not only does a good tech have the experience to deal with this type of problem, but they have equipment that allows them to look at things the average consumer can’t see, and a collection of replacement parts they can use to quickly test individual components on your machine.
Do this
Subscribe to Confident Computing! Less frustration and more confidence, solutions, answers, and tips in your inbox every week.
I'll see you there!
Podcast audio
Related Video
I like your advice to plug in another monitor. I had to find this out by trial and error and now find this laptop runs quite well with a separate monitor. It only works though if you find the right setting on the CRT/LCD switch. I found this out the hard way too.
I found that the most common failure is the power supply in a pc that has fans running but no beep. These supplies even test good (I don’t have a load tester) but when replaced, the system comes right up. In fact about 9 out of 10 systems I see with bad power supplies have this problem rather than just being completely dead.
I repair computers for a school district and see this 3 or 4 times a week. (We have quite a few computers that are more than 3 years old).
I have found that inline power supplies are often at fault, even so called robust ones. With the PC turned OFF turn the monitor OFF, then after 5 seconds switch on again. You should see “No Input” even if its not connected and the PC is off. It will disappear after a fews seconds. If you see this message then the computer graphics section or card is probably faulty. Try the monitor on another PC.
Another problem often overlooked is power strips which have power save sockets ( save the earth etc !) , i.e. 1 or 2 sockets are for the main unit, i.e. the computer itself but the others are for monitors, printers, routers etc. When the computer is switched on the circuitry built into the power strip “senses” the load and turns all of the sockets ON and everything powers up. When it is switched off all the other bits of gear also switch off.
HOWEVER… quite a lot of these strips fail or don’t quite do what they should and one or more of the sockets remains OFF, I have one such strip. If the monitor is plugged into it no power is made to the socket and the monitor stays off no matter how much I swear at it or pray to the intel god’s etc etc. Simply remove the monitor from the strip and plug it into a known to work wall socket.
Laptops often don’t beep at all. My personal laptop works great but once in a while if I unplug something from a USB port by accident when moving the laptop, when I turn it on the screen will stay black as a safety precaution for about 10 minutes and the capslock button will stay lit blue, in this case all I have to do is wait 10 minutes and reboot and the computer will run normally again. I first noticed this because one day I dropped the laptop and was worried that the LCD power Inverter broke but after 15 minutes it worked again. I found out its a built in safety feature that keeps the screen from coming on right after some type of trauma or action(such as removing the running external hard drive).
9 out of 10 I find it to be the power supply
You are right.. 9/ 10 it’s the power supply. I had the same problem with my machine and “walah!” Now it’s running great.. thanks Mr Rogers for the one line solution.. and thanks Leo for this blog..
When this happens I always disconnect all USB devices, except keyboard and mouse and try the reboot again. I can’t even guess at the number of times I have seen something on the USB bus cause this. From flaky web cams to corrupted printer drivers the problem is always the same- PC seems to boot up but the display never comes up. If that’s it, it’s just a matter of plugging in one at a time and rebooting until the problem either clears or you find the suspect device.
On my laptop there is a small pin that is pushed down when the lid is closed; this shuts off the screen display. Sometimes it sticks down so the screen doesn’t show anything. A pair of tweezers (or some other suitable gizmo) can be used to prise up the sticking pin.
I hope it is that simple for you.
I had the exact same problem that contimued for a few weeks. I would have to power off for a few minutes and power back on and the problem would usually go away. Later, because of “time” display probems. I installed a new battery…and this fixed “both” problems.
I have an IBM ThinkCentre running Win XP Pro.
Occasionally when I turn it on, the monitor stays black, the fans and normal computer sounds seen to be twice as loud as normal. I hold the power button down and turn it off. I wait a few seconds and turn it back on. it does the same thing. I learned this, that when this happens and I turn it off, if I then UNPLUG the power cord, then plug it back in, the computer comes back on for a few seconds, then turns itself back off. Now when I push the power button, it will boot up normally.
Thank you Leo for all th info U give us not-so- bright pc users.
I get frustrated when I press th ‘power on’ button several times before it will power up th pc. Also had it not to shut down until I unplugged it…..jt
I have Windows 7 and sometimes it can be frustrating. I also turn it off for a few minutes and power back on as Mike R does and it works for me too. But it still scares me when I hear of all the computer crashes wherein you lose everything. I have a separate external hard drive but I have not yet figured out how to smoothly save to it. I wonder if I should replace the battery like Mike did.
remove ram, boot and see if beeps occur.Replace one stick at a time.
jp
I had the same problem a year or so ago.
Somehow some of the connections on my add-on video card had come loose form the circuit board. I have no idea how that happened but it was a fustrating weekend figuring out what was worng.
Thank you, Leo, and everyone for a very useful article and commentary.
A year ago a friend came to me with a computer in this condition. I tried changing the video card without success and almost gave up. He insisted that it happened after he had tinkered with some setting. “Could it be the BIOS?” I asked myself: I had never seen an entry there for switching off the video output. Nevertheless, I tried removing the battery and shorting out the contacts for half a minute to flatten any residual charge, as well as using the reset jumper, to restore it to the default settings. Much to our amazement, upon restarting all was back to normal!
I had this same thing happen to me, traced down to a dead power supply. I changed it out and all cam back OK. (CAUTION) Voltages in power supplies are very dangerous, do not attempt a repair. Power supplies are very cheap Very easy to replace not worth your life.
In regards to the beep codes, newer laptops can now have flashing light codes instead of beeping. All the lights, power, caps lock, num lock etc flash at the same time in patterns similar to beep codes
For God’s sake, folks — yes, even you, Leo! — if you don’t see anything on your monitor when you start up your computer, the absolutely very first thing you should do is to check that your monitor is plugged in, that it is turned on, and that its cables are tightly connected at both ends.
IMPORTANT: And yes, I did say “cables” — plural — because a monitor has TWO cables! One carries the electric power, and goes from the monitor to a wall outlet or power strip; the other one carries the video signal and goes from the monitor to the computer. You must check them both, because a failure in either one will certainly mean a dead monitor! :)
Hope this helps! :)
I work in IT and found this same thing happening to many of our PCs. I found a simple fix for ours. First, unplug the PC. Then, hold the power button in until there are no more lights showing or any sounds. Then plug it back in and you’re ready to power up. This fixed the problem and it didn’t reoccur on those PCs.
It was my video card when this same thing happened to me. Sorry I am just now adding this, but I have been dealing with a new computer and haven’t had much time to read all my emails.
i have this one too. . the monitor is OK cause i used it to my other computers . . just the CPU. . video card is OK ..RAM is OK . .power supply is OK. .so i see its the mother board this time . . i changed it immediately. . then its OK. . mine works. .repairing comp is just an easy task to do if you have equipment . .so i say if you aren’t sure just get a tech to help like LEO said. .^^ hope it helps. God Bless and good luck!
My computer gives more than one beep it gives three beeps, what coul be the error
Check with the computer manufacturer. BIOS beep codes can be machine specific, but often indicate something.
I just build a custom pc. It has a gtx 760, 8 ge of ddr3 ram, Intel i5 4670k, MSI Z97 Pc Mate, thermal take 600w. So I put it all together and I powered it up lights come on and fans run and I understand that that may not mean the power supply works. I have tried everything out there. I Googled this issue many times found the same fixes and tried them. Nothing works. I don’t know what to try now. Please get back to me.
Hi
I tried to add another 80 Giga internal HD to my computer with XP OS, the system and fan run but no beep and monitor is black.
Removing the internal HD didn’t help and still the system is screwed up.
Any advise is greatly appreciated.
Hose
Simply unplugging the power cord and press the power button for 2mins. Replug the power cord and you are okay. [Sometimes].
Mr. Leo if u can help. I’m laptop keeps crashing mostly when its plug. It seldomly crases in safe mode and on battery. I clean the heat sink and replace the fan. But still.
I have a hp pavilion dv7-1103ea laptop and when I turn it on – all the lights come on on the casing (light next to caps lock and at top of end and Pg up both flash), and the screen remains blank and takes up to 15 minutes before the screen all of a sudden comes to life! Any ideas please? The date is correct, but the time was an hour behind.
Thanks in advance. Monya
Hay, first of all I say thanks to you for such great details and I want to ask a quarry about my system
First ) when i start my computer with GPU is sound 1 short beep which is OK but did not get any display all things starts up all fan spins GPU fan also spins
My GPU is working in my friends comp.
And other low level GPU in my comp. It work my motherboard is g31m es2l rev1.1 and my GPU is gt 730 v2 gddr5 1gb plz help me sir.. I really In tension
thank you so much for that article it really helped. I think I believe my computer is fried, no beeps, the power light goes on, the fans go on, but nothing comes on on-screen, time for a new computer! thank you,very helpful. Jay
I got a probblem with my acer aspire 5745 after bios update and changing settings my laptop only flashes power,numlock and capslock lights non stop but never turning up what should I do
Guysss pleaseee help me!
What ticked me off was my USB keyboard disconnecting and reconnecting constantly… Followed by the windows prompt sounds..
So Much so I couldn’t do anything without getting angry! Gaming typing music nothing!!
I looked up for a solution on Google n many many other sites but…Nada :'(
Most solutions involved buying fresh new hardware.. Where as I tried multiple USB keyboards but nothing changed..
Finally I try one more thing.. (I wish I hadn’t)
Uninstall the USB hub or something in Bus controllers.. So that it gets reinstalled on rebooting.
BUT NOW MY PC JUST WONT BOOT..
Just two beeps! :'(
Should I try fiddling with the internal hardware components.. RAM n stuff??
Help is appreciated!
Cheers!
Solution fo recovery bios Dell N5110
1. Download the latest firmware from the Dell support
2. Save the .exe and create a shortcut with the following parameter: ”
/writehdrfile” by right clicking the shortcut icon and going into the properties
menu.
3. Run the created shortcut and it will create a n5110a11.hdr file rename the file
to N5110.hdr
4. Create a shortcut .exe file with the following parameter: ” /writeromfile” by
right clicking the shortcut icon and going into the properties menu.
5. Start the created shortcut and it will create a n5110a11.rom file rename the file
to DQ15A11.rom
6. Copy both file “N5110.hdr” and “DQ15A11.rom” to a FAT formatted pendrive’s root
folder
7. Remove the charger and Battery from the laptop
8. Plug In the pendrive
9. Press & hold END
10. Connect the charger (still hold END)
11. The notebook starts automatically and shows the recovery screen
12. Press enter and wait until finish the flashing
13. Press esc to restart
14. Hopefully problem solved
when I on my monitor and CPU …the CPU works properly but my screen didn’t show any thing,when I lighted with torch on screen …it show but very lightly….
Sounds like the monitor is broken. Try another one.
I have my dell Latitude E6500 laptop and the mouse is always randomly moving diagonally over the screen.I need to know how i can be helped.
Here are a couple of articles which might help you diagnose the problem.
https://askleo.com/why_does_the_mouse_pointer_jump_around_the_screen/
http://ask-leo.com/could_my_mouse_trackpad_be_causing_my_cursor_to_jump_around_the_screen.html
I have a laptop windows 7 computer. it is about 3 years old. last night i was on line and all of a sudden it made a loud noise and screen went blank. i pushed the off/on button to shut it down. after a min i turned it back on. all the lts on the key board came on but the thing that would come up on the screen was a white file strip saying windows is loading files. then the screen would go blank and come on and say micro soft corp and go blank again then come back on with only a very bright blue screen. i always sat the computer on my lap and about an hour before it went down,i almost dropped it but it did jerk. could you,leo or anyone out there help. thanks
Sounds like something broke – physically. You’ll likely need a technician to diagnose it.
i changed my power supply of my PC after it could not start now its spinnng everythng inside but no display Im confused now
I have a Lenovo T400 that turns on but nothing happens eventhougth the fans turns , the hard drive spine, the memory is ok since i have tested it in another laptop. then somethings it comes on and function well without ceasing, then when you put it off, it won*t work at all again,, pls i need help,
It’s not possible to diagnose a problem with just that information without looking at the machine. You’ll probably have to bring it to a technician to look at it.
when i turns on the power switch, the PC does not come on and i cant hear the fan, there is no power light on and i hears no beeps or other sounds coming from the system……… WHY?
That almost sounds like it isn’t plugged in. The first thing I would do is check the power cord. Sometimes they can jiggle loose.
was playing a game on my dell latitude e-6500 den it got freezed up so i unplugged the ac so as for it to go off, removed the hdd for few minutes reinserted the hdd plus the ac and tried rebooting but only the fan wil start turning then stops power light goes off, and I am left with solid Caps and Scroll lock lights and a flashing Numlock light. please tell me what to do. thanks in advance
You probably need to take it to a technician for diagnosis. This sounds like a hardware failure of some sort.
Um hi i just get here got a question when i turn on the AVR monitor functioning but when i turn button on it did’nt show any display again my keyboard didnt work but mous and dvd player are functioning???
Someone know how to fix this?
sir i my hp pavilion g4 laptop lcd broken and i change it butt screen is lack i attach old lcd this time old lcd remain black i change the video cable but the screen remain black no wifi light show on keyboard and also capslock light is not turn on on pressing.
I have an HP Pavillion h8-1214, w/AMD FX-6100 Six-Core processor, 10GB DDR3, Radeon HD 7450 graphics card w/1GB DDR3 dedicated memory, and a 1.5TB HD….oh and a Blackweb keyboard. I was using the computer last night and it was fine. I woke up this morning it was in sleep mode, as it should be. I usually tap the space bar to wake it up and the keyboard should light up, the mouse and the monitor as well, while the computer roared to life……except NOT this morning,
The tower lit up, by the power button and the disc drive, but that is all…no wifi light or yellow disc load light. I used the kids’ computer to look up causes/fixes.
I tried a Linux Live CD, to diagnose, and I disconnected the HD, and used the flashdrive that I downloaded FalconFour onto…..it powered up the monitor, keyboard and mouse, but it wouldn’t go any further…”No boot disk has been detected or boot disk has failed”….I disconnected the FD, and reconnected the HD, turned on the power, and same as before. Shut it down (by holding the power button down) and reconnected the FD, and I wouldn’t get the same results as the first time…dead.
I also disconnected the mouse, keyboard and monitor……if the HDMI for the monitor is disconnected, the monitor says check connection, so I plug it in, then it goes pitch black. The keyboard, when I plug it in, flashes for a second, then nothing……….fans run but minimally
I NEED help!!
So what if your PC makes no beep at all when it starts? For the life of me I can’t recall it ever making a beep when it was successfully running, but I can guarantee it’s definitely not making any noises now. Any ideas?
Only what’s outlined in the article.
Our desktop computer works perfectly fine and never beeps at all.
Go figure.
Maybe it’ll beep when something’s wrong — but that’s not something I’m eager to find out!