Quote Originally Posted by Grinenshire View Post
Check that your fans aren't too dusty. This happens quite a bit especially with laptops.

As for the test, do an experiment. Run a high-end 3rd game at full quality and see when it turns off. Then restart the PC and leave the empty desktop open for a bit. If it goes off on the first but not the later, it's the overheat.
The more demanding the task, the more power your components will draw from the PSU, so this test won't work.

It's probably quite likely it's overheating. Try <a href="http://www.majorgeeks.com/download.php?det=311">this</a> piece of software that will give you information about stuff on your motherboard, like temperature and voltage sensors. Run it immediately after a crash and let us know what it says.