When my computer was giving me BSODS and studdering after a few hours of heavy use, I installed 2 140mm fans in my case. No problems since. The fact he was watching movies at that time is probably just coincidence.
How many do you have? If you just have 2 fans (one in the back, one in the front) you need to get more. A system like that is just naturally going to be hot. Make sure the ones you currently have in the case are installed correctly. There are usually arrows on the fan. The one in the front is supposed to suck air in, and the one in the back is supposed to blow air out. The one on the side is also to suck air out. In my case I have 2 140's on the top also sucking out, and a 120 behind the processor sucking. lol. sucking and blowing.