The fix is generally to completely remove the previous driver
(and the nvidia control panel)
Using this utility in safe mode - Phyxion.net - Driver Sweeper
Then reboot normal and reinstall the latest driver again.
This actually happens often in all versions of windows and with both nvidia and ati.
The main problem is ..well if there is a problem their uninstallers/installers don't actually function quite the way they should.
Anyhow give that a shot and see if it cleans you up.
If not we'll go to the more complex steps.