My computer keeps restarting

You can try a different Windows startup option to debug this.

When your computer is booting up, right after the last BIOS message (right before Windows starts to boot), press and hold the F8 key. This should bring up the Windows startup menu. You can try booting the last known good configuration and see if that gets you anywhere. If not, you should boot into safe mode and, assuming that works, investigate some things.

I don't know what version of Windows you've got, but typically you can right-click on My Computer and select Manage. From there, you can click on Event Viewer, then System, and you'll see a list of system events. You can look at the events and double-click on them to get a little more info. Sometimes you'll see something useful there.

The other thing you should do is to change the system settings so that the computer doesn't immediately reboot when it encounters a problem. Again, this varies according to what Windows version you have, but you can try right-clicking on My Computer, selecting Properties, then click the Advanced tab, then click on Startup and Recovery settings, uncheck the box that says "automatically restart", then click OK (twice).

Then, reboot normally, and you may get to see a blue screen (known as a BSOD), which may display an error message that you can then do a search on to find out possible solutions.

If none of that helps, then you may just need someone with lots of Windows PC knowledge to look at your PC and help identify and fix your specific problem.