Black Ops Desktop Crash Problem

Hello there, as am addictive to black ops I can't stay one day without playing it, lately I faced some problem which I hope you can
Help me with, please.
The second mission black ops desktop crash , I tried everything I can, I have GTX 570 latest drivers, I did "Custom" clean install of the drivers, I removed all NVIDIA Display driver components and reinstall.
Nothing works, any suggestion please.
And thank's anyway.
