it also happens to me before randomly (early this year before the patch) and i used to suspect due to overheating. I tried playing only one game at a time - meaning after one game, i would turn off my pc or close the game for a while, and then after few minutes or hours i will play again.

but the weird thing is it happens only to 2k11.
so far it doesnt happens again.

I also found some sites stating it might be some problem with your Settings file, but i am not sure.
Hope this helps
