Random Restarts?

Anything like this happened to any of you guys? I load up a game, any game, doesn't matter which one (fullscreen though) and then anywhere from 1 to 30 mins into play my screen goes instantly black and me comp has just rebooted. I know a quite a bit about comps but not enough to have any idea wtf could be going on. Help meh!
Tried: installing latest video driver, fixing errors in event logs, and running games on lower settings...all with no luck.

Either your comp is overheating, or else your PSU is failing/too weak.

I had the same thing - my RAM slot was acting on me after a while. Too close to heatsink? Possible.

Now I have only 2 working slots ;_;

www.opera.com

Either you're overheating, youre RAM is mismatched, or your PSU is in trouble.