It’s best not to read too much into available memory. Windows memory management is the stuff of nightmares even for the people who understand it. For the rest of us, it’s just magic.
There are many reasons a computer might get stuck continually rebooting. Fortunately there’s no need to lose data. You have several ways to get your data off there and with a little bit of luck you may get you a working system again as well.
Quite often the first thing that a diagnostic technician will ask you to do is reboot your computer. Why? Because rebooting works surprisingly often.
Random reboots are annoying because you can easily lose what you’re working on at the time. Random reboots are difficult to diagnose, because there are many possible causes.