My computer lights up and turns on but nothing happens, why?

Diagnosing a computer that won't boot can be very difficult. In particular, spinning disks and blinking lights don't mean as much as you might think.

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I’m having problem starting up my computer. When I press the Power button, it lights up and everything inside it runs, but nothing appears on my monitor. I don’t know what’s the problem. I already cleaned it and had reset the CMOS, but nothing works.

Well, I’ll put it this way: just because the lights are on, doesn’t mean anyone’s home.

I get this and similar questions often. You turn on your computer. It makes noise, you can see lights – perhaps even blinking lights – and assume that it must be running.

It might be.

Problem is – it might also not be running at all.

Lights and noise mean … nothing, really

The phrase “everything inside it runs” is actually impossible to prove just by looking.

You might very well hear the fans all start to blow, disks might start to spin, and you might see some lights come on, but about the only thing that you can say by all of that happening is that the computer has power.

…don’t read too much into blinking lights, spinning disks, and running fans.

I’ll put it another way; if you actually removed the CPU or the RAM (don’t), the fans would blow, the disks would spin, and some lights would come on.

And the computer would have exactly zero chance of actually working.

So don’t read too much into blinking lights, spinning disks, and running fans.

The good news is that the computer appears to have power. The bad news is that you simply can’t assuming anything more.

Did it beep?

One of the more underrated and useful diagnostic tools for problems of this sort is the beep.

You know, the single beep your computer makes after you turn it on?

That beep is generated by software; specifically, the BIOS installed in your computer.

If you hear the beep, that tells you that the CPU is working, the BIOS seems intact, and at least some RAM is working.

That’s a start.

If you don’t hear that beep at all … well, then you have problems. One or more of the CPU, RAM, motherboard, or some other component isn’t working. In fact, it could still even be the power supply.

Open Desktop PCBeep codes

If you hear more than one beep; if it sounds like your computer is beeping out a Morse code letter with multiple short and/or long beeps, then it’s trying to tell you something.

It’s trying to tell you that something isn’t working.

The POST (or Power On Self Test) has detected a problem and is using a pattern of beeps to try and tell you that something is wrong. What beep codes mean unfortunately depends on the BIOS manufacturer. There’s a fairly comprehensive list “_blank”>here.

Why beeps? Because the BIOS may have detected a problem before turning on its video display hardware and software. Or the failure might have been in the video display hardware. With no way to show you the problem, beep codes are the only way that BIOS has to talk to the outside world.

One beep, but no display?

If the computer gives you that one “all’s 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, that it’s connected, and that the connections are good.

If everything looks OK, 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 that it’s your monitor or cable that needs repair or replacement.

If it doesn’t, then things point back to the computer itself. And unfortunately, while you might prioritize looking at the video card as the most likely suspect, pretty much anything from RAM problems to power supply problems could still be at fault.

Sometimes, you just need a technician

Just like you sometimes need a mechanic to repair your car, sometimes you do need a technician to diagnose your computer. Not only does a good tech have the experience to deal with this type of problem, they also have the equipment that allows them to look at things the average consumer can’t see, and a collection of replacement parts that they can use to quickly test individual components on your machine.

There are 20 comments:

  1. Malcolm Crocker Reply

    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.

  2. CJ Mac Reply

    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).

  3. mike @ multilink Reply

    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.

  4. S3curityPlu5 Reply

    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).

  5. JimH Reply

    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.

  6. Peter Lawrence Reply

    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.

  7. Mike R Reply

    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.

  8. G. Daniel Reply

    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.

  9. jerry thomas Reply

    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

  10. Jack Ragan Reply

    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.

  11. johnpro2 Reply

    remove ram, boot and see if beeps occur.Replace one stick at a time.
    jp

  12. Snert Reply

    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.

  13. Bernard Winchester Reply

    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!

  14. William Franks Reply

    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.

  15. Jeffrey Reply

    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

  16. Glenn P. Reply

    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!           :)

  17. Nancy Woll Reply

    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.

  18. Vicki Reply

    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.

  19. Edward garcia Reply

    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!

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