fps lag

Hi, i got very anoing problem with my FPS lag, it's happen, i think when i install COD BO, after that i try everything, i reinstall et, delete COD BO, made new cfg, reinstall drivers, delete et foder and reinstall fresh one, i try without any cfg, but nothing, then i buy new network adapter and cables, then i reinstall xfire, slac and other stuff, and it's not helped, after all those things i reinstall my windows, with FORMATING HDD, and when i indtall et, guess what, i STILL HAVE LAG, it was 125FPS now always 75 and thats just anoing. WHAT can i do?:s