A little while ago i noticed that my computer had started to restart or completely shut down on its own randomly when i was using it. The computer has gotten slower over the years (its about 5 years old) and when i shut down on its own again today i decided that i would just reformat the whole thing. So I just finished doing the disk recovery thing and i transferred over some old files that i had backed up from before onto another hard drive and I was just installing a game back onto the computer a few moments ago when the computer restarted by itself again! when it came back i started my browser and it did it again a second time. Anyway I was wondering what the hell is going on with this thing, could it be some of the files i backed up and transferred over? Im running windows XP any additional info you guys need about the PC or what i have on it ill tell you, but please I really need some help I cant have this happening over and over again. please help guys, thanks.

With the age of the computer, the first thing I check for when these symptoms start showing up out of nowhere (even after a clean install) is bulging capacitors on the motherboard. Carefully examine the capacitors on your board and see if you notice any bulges in the top (they should be nice and flat) or possibly even some residue on the top of them (could be brown or black in color). If you see any capacitors like this you have 2 choices: replace the capacitors by soldering new ones in place of the old ones or simply replace the motherboard.

The power supply is also another suspect. While not nearly as common, I have seen bulged capacitors in power supplies as well... but they usually fail in other ways that can also cause your symptoms. If you don't notice any bulged/leaking capacitors on your motherboard, I'd try another power supply to see if that makes a difference.

I had a problem with my computer shutting down constantly and replaced my power supply but I put a cheap one in and it soon went out too. I then replaced it with a very good one with more watts and while I was at it I cleaned out the inside because I noticed it was extremely dusty and the graphics card had a TON of dust built up on the fan. Ever since replacing the power supply and cleaning it out I haven't had a problem since.

I am also wondering if you might not have a virus in your system somewhere, could even be in the boot record. The Blaster worm shuts down the system like this and if you don't have the updates to prevent it your computer will get it on the Internet right away.