Sound like this could be a hardware problem with your Nvidia graphics card.
Also,did you go to Nvidia"s site to get the latest drivers?
Could you give us the exact make nd model of your video card.
Go to Start, Run, and type msinfo32, expand the Components section and look under Display for that information.
This program will give you detailed info on your machine if it is not available in msinfo32
http://majorgeeks.com/SIW_System_Info_d4387.html