did you update windows before this happened?
First, uninstall the NVIDIA drivers (if they are still installed) using Programs and Features. You can get to Programs and Features by clicking on the Vista Orb, then clicking on Control Panel. Then click Uninstall a Program. Once in Programs and Features, you need to find NVIDIA Drivers and click Uninstall/Change. Make sure the NVIDIA Display Driver checkbox is checked, then click Remove.
Next, please download and install Guru3D Driver Sweeper from here. (Click on the Download (Europe) link, then scroll down and click on I Agree.)
Then, boot the computer into safe mode. To do this,
Turn the computer on (or restart the computer if it is already on).
Start tapping the F8 key. The Windows Advanced Boot Options Menu appears. If you begin tapping the F8 key too soon, some computers display a "keyboard error" message. To resolve this, restart the computer and try again.
Ensure that the Safe mode option is selected.
Press Enter. The computer then begins to start in safe mode.
Next, open the program, Guru3D Driver Sweeper, that you just installed. Check the checkbox for cleaning NVIDIA - Display drivers. Then press the Clean button.
Reboot normally (not into safe mode), and then, download and install the drivers found here.
Reboot when prompted, and let us know if you still receive the error message.