Did you do a fresh install of Win7 x64, or some kind of Upgrade from Home x86 to Pro/Ultimate x64? I never like doing upgrades. Too much residual crap can be left behind that causes problems. If you have done a fresh install then you can either try one of the "Driver" fix programs to figure out which driver or drivers are the problem, or simply backup your data, try a fresh install and slowly over time install updated 64bit drivers on your system. Sometimes, all upgraded drivers are not good updated drivers (due to the many hardware configurations in the PC arena).