I have black ops 2 core duo problems with constant fps.

I have black ops 2 core duo problems with constant fps drops in it.
I have updated my NVIDIA driver (videocard is GT430 1024MB 128bits), my pc I working well, and playing CoDMW2 MW3 or ACIII I can easily get over 100 fps.
However, with black ops (CPU: Core 2 Duo E8400 2.40GHz @ 3.00Ghz) I have 70-80 fps and even it falls to 40-50 or less, even to 30, and sometimes everything crashes.
I am grateful to those who could help me.
