If the driver got corrupted somehow it could cause this. I find it unusual because this used to be a huge problem with XP, but more recently it's become less frequent to see and I rarely see it at all with Windows 7.
Download this program and use it to remove all NVIDIA graphics drivers for the system. If you had ATI or some other manufacturer drivers installed some time in the past, then be sure to remove those as well.
http://www.guru3d.com/category/driversweeper/
After that completes be sure to reboot before attempting to install the appropriate NVIDIA driver.