Do you know what graphic card you have from nVidia?
Go to:
www.nvidia.comunder Download Drivers > Download Drivers Dropdown > Manually find drivers for my NVIDIA products.
Select your correct product type and series, OS and you need to know if it's either 32 or 64bit.
Search and download the latest drivers. It's quite a large filesize ~100MB.
For example:
Version: 197.45 WHQL
Release Date: 2010.04.13
Operating System: Windows Vista 64-bit, Windows 7 64-bit
Language: English (U.S.)
File Size: 117 MB
Once downloaded try run that to install, any luck?