System Freezes after I exit BIOSHOCK or Crysis 2 since GTX 560 install

Hello,

My system is freezing whenever I exit Crysis 2 or Bioshock and when at idle for long periods of time. This just started happening when I installed the new video card. The onboard video is disabled. When playing the games, they play great! No slow downs at they look awesome at full specs on both games and have also at max resolution of 1900x1200.

this system is NOT overclocked.

My current rig specs are:
OS - Win 7 64bit Ultimate
Dell wfp24 24" display
MB - Intel DG43ID
PSU - Antec Tru Power II with LED 480
Proc - intel Q9550
Ram - 8GB
HD - 500 GB SATA II
Video - EVGA 560 (Non-ti) 2GB superclocked with latest drivers.
DX 11 is installed too.