Stop playing games. Throw your computer from a 20 storey building.
Then take up healthy outdoor activities and sports, such as the Triathalon. Try to engage in these activities when it is especially cold and miserable, it will do you good. It will build character. It will make you a man.
Don't drink Coca-Cola. Eat lots of lettuce and horse radishes. This will give you keen insight into the World's problems. Be prepared to vote. Celebrate your freedom yet control your inner urges and only wear comfortable clothes.
You know it makes sense.
Definitely sounds like overheating. Get yourself some temp monitoring software, such as Motherboard Monitor or check your motherboard CD for hardware monitoring software. Do as reefy says and take the side off your case. Run Prime 95 and see if it crashes. Also, set up a desktop fan and have it blow into the side of your case (with side off) when you play games, that'll keep it cool. If it no crash, things is too hot, consider a new CPU cooler.
If it still crash, consider a fresh install or even a new machine.
This advice, given in all sincerity, courtesy the Balham thought police.
Time for my meds now, I think.