[adanthar]

-The CPU fan is dead or dying and needs to go, like, now, unless you do not have it connected to the MB sensor.
-The system fan or the motherboard fan connector is also kinda screwed up but (probably) isn't causing your problem.
-50C is a good temp for modern processors after, say, 4 hours of Doom 3. 60C is way pushing it. Higher than that and you're eventually going to fry the chip unless it automatically shuts down, which it sounds like it's doing. Don't even bother running it anymore until everything's replaced.