Completely uninstalling graphics drivers(works for both nvidia and ati drivers):
1)Uninstall driver using Add/Remove (Programs and Features for vista) from the Control Panel
2)Install Driver Sweeper from <
http://downloads.guru3d.com/Driver-Sweeper-beta-2.0.0-downlo ad-2186.html>
2)Reboot in safe mode: press and hold F8 while your computer boots up (You should get a list of options if you’ve done it right) and select Safe Mode from he list.
3)Run Driver Sweeper while in safe mode and remove any leftover traces of the graphics card driver
4)Restart computer into normal mode and install your new driver