ComputerBB

Hey guys. It's almost Christmas, but I'm a little low on holiday cheer.

You see, my computer's been mysteriously turning itself off. There's no shutdown screen or anything, it'll be running fine and the next second it'll be off. Some apps seem to trigger it (mostly games), and it'll also shut down sometimes even if none of those apps are in use. The problem seems to be getting worse, if that's possible; it's more likely then before that it'll shutdown even if nothing's running.

Compaq Presario 5000
1.3 GHz Intel Celeron
256 MB RAM
XP home edition

Here's what I've tried so far:
1. Last known good configuration.
2. System restore.
3. Factory restore.
4. Scanned with Norton & Spybot; both came up with zip at first, and after the factory restore they can't even get through a scan without the system shutting down (even in safe mode).
5. Turned off the "automatically restart" tab in "startup & recovery."

I have no clue what to try next. I don't even know if this problem's caused by a virus, some OS problem, or something else entirely. Any ideas?

reset the CMOS and update your video drivers