Computer turned itself off and restarted, WHY?

[Bignate603]

I was in the middle of sending a very large file to a friend with a very slow modem my computer TURNED ITSELF OFF. I was chatting with my friend one sec then looking at the bios checking my disk drives the next. Went right off then restarted. I know it's not the powersupply, that's a 330 enermax. Could my processor be running to hot? would that cause it to just restart?

 

What OS?
My win2k did that like once after not rebooting it for about 25days or so.

 

[Bignate603]

winME after being on for a few hours, lol