The following are the steps that I follow and they work all the time, I hope they help you too:
1. Download the the driver from Nvidia web page for the OS installed on your box
2. Go to GURU 3D and download DDU Display Driver Uninstaller
3. If you are using Nvidia control panel to handle your AA and Sync and other setting write them down
4. Run DDU and select Safe Boot and full uninstall to fully clean and remove old video drivers.
5. Login in safe mode and DDU will run automatically, reboot and login with normal windows.
6. Run the driver install from Nvidia and make sure you select clean and full install.
7. Reboot, login again and then go to nvidia control panel to enter the settings that work for you.
and that's it.