I lag when I shouldnt! Please help!

Hello everyone. I recently built a computer and all went fine until i downloaded Call of Duty Black Ops. When ever I try to play with game maxed out I get 6 frames per second? I had to reinstall the game again because I had to wipe my hard drive from an error. I can play MW2, GTA IV etc... All at max setting at 50+ frames per second at 1080p. What is going on here? System specs are below.

AMD FX 4100 OC 3.9GHZ

EVGA GTX 550 TI FACTORY OC

WD CAVIAR 500G

MSI 970A-G46 MOTHERBOARD

ULTRA 750W 80+ POWER SUPPLY

PATRIOT G2 4GB RAM