I'm having computer trouble?

I'm having some computer trouble. What's happening is that every time I try to place a game on steam, or actually any non browser game, after 10 minutes or so the computer just turns off. The computer is plugged in so it's not running out of charge. I don't believe its overheating. This happens every time I play a game, no exceptions. I own a Sager laptop. Not sure of the model.