My problem was all of my games would freeze after a few minutes of play. I gave my computer back to my techie and he tried everything. When the only thing left was the processor, he switched it with a 500mkz and put mine in the other machine. Bingo, nothing happened. He gave it back with the 500 in it to try. First game I fired up was Unreal I played for an hour without a problem, next Sims, next RTCW no problems at all. We replaced the 500 with a new 900 and still no problems at all.
The first thing to check is the processors temperature. If it’s too high your probably burning it out. Mine was running between 170 and 180 degrees. Hope this helps someone.