I have a confession to make: I enjoy the Call of Duty series. Some may scoff and hit me with a splash of Haterade, but the fact of the matter is, there's something that remains consistent with each new game in the series: I have fun. Fun is the operative word here, because while the series, like many others, has its obvious faults, what I care about most is whether or not I'm enjoying the game, and am intrigued enough to carry on. So far, no Call of Duty has let me down.
...and with this completely helpful comment....let me help you (The OP).
To OP: What is your CPU? If it's lower than Intel Core2 Duo E8200 2.66 GHz or AMD Phenom X3 8750 2.4 GHz then you're not meeting minimum requirements.
If it's equal or better then you can try the following (as this sounds like a software issue).
- (re)install the latest nvidia drivers (at the time of this post, nvidia drivers v310.xx)
- If that doesn't work, reinstall the game (through STEAM)
- If that doesn't work, contact Steam and/or Activition support because things should work.