Have you tried opening My Documents or something and typing in the location into the address bar of the window.
ie: c:\windows\system32\dllcache\control.exe
or just c:\ for the hard drive

Might work and let you into control panel so you can have a look at your settings.

Can't think of a reason for this other than the GFX install, but if you have restored the system (doesnt always work I know). Try downloading a reg cleaner from the downloads section of this site and clean the reg, might be some left over files from the GeForce.

Let us know how you get on.