Your CPU's overheating. I had the same problem. Tried all of the suggestions on video card and such, but to no avail.
The mobo is shutting down (you see this setting in config) because you are overheating. Either you have a fan that has gone out, not functioning properly, or something to that effect.
Best advice, take it in before blowing out your mobo and video card, also install a 2nd fan.
