Oh no, you got the infamous infinite loop problem. You say it only occurs during games? OH, well you are not alone.
First make sure you are providing enough power for it, make sure you have at least a 300 watt power supply. Also for some people, something that has worked is setting your agp speed to 2x instead of 4x, you can do this from your computer bios. If that doesnt work, that best thing you can do is quickly go to the store, return your video card, and get another one preferably with another gpu or brand.