Hey guys, I feel that my PC is slowing down, do you know a reason why?

My PC has 2G of RAM, a nVidia 9500 GT, an Intel Dual-core processor at 1.6 Ghz and an ASUS P5NSLI for a motherboard. I play CoD4, MW2 and L4D2 with it. My gameplay used to be smooth until I switched to the ASUS motherboard. I read in the 'net that P5NSLI-s doesn't have drivers for Windows 7 but its drivers for preceding OS still works so I had the drivers installed anyway. I'd really appreciate any help. I love my PC, and I devoted a lot of time and savings to build it and it just hurts to see it just slow down like grandpa.