Quote Originally Posted by Omecle View Post
How would I know if it's overheating, or just not giving enough power?
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.