Motherboard and Cpu change lag-low fps problem

[GLOBUS]

Hi!i have just changed my mother board from Asus to Gigabyte P35C-DS3 with cpu Intel core 2 Duo e6850 3.00GHz and graphics card-Nvidia Geforce 9600 GT 512mb.I made a clean install of windows again so i dont have any problems with the drivers.My problem is that games that i used to play like (Call of Duty modern warfare 2) now lag and have low fps.I used to play those games with my old asus motherboard and same graphics card with cpu Intel cored 2Duo e6600 2.4Ghz but now they lag.Is there something i can do with that?my (ram is ddr2 5gb)

 

[popatim]

Did you reinstall windows and all the new motherbds drivers?

 

[GLOBUS]

yes i did