Do this thing.......
Download the latest drivers for your video card.
Go to Guru3d and get Driver Sweeper
Driver Sweeper (no install needed)
Guru3D - Driver Sweeper (no installer) download from Guru3D.com
Open up your C: partition and find the NVIDIA Directory (should be in C: unless you have multiple drives/partitions and you installed in one of those), open the folder named WinVista64, you should see a driver version folder (177.79 for example). Leave this window open.
Vista
1. Right click on Computer---->Properties.
2. Click on Device Manager.
3. Expand Display Adapters.
4. Right mouse click the video card name.
5. Select Uninstall, select "Delete the driver software for this device"
6. Do not reboot/restart.
7. Now go to the window you left open earlier with the NVIDIA directory. Delete your driver version folder (Example 177.79). Empty Recycle Bin.
8. Restart in Safe mode (Use the F8 key while your rebooting to select Safe Mode).
9. Now run Driver Sweeper
10. Make sure you select "Remove your NVIDIA Display Drivers" once it is finished. Do not remove your chipset drivers.
11. Reboot. Upon restart Vista will install a generic VGA adapter.
12. Now install the latest video drivers for your card.
13. Once it is finished installing restart your computer normally.
This should resolve any driver issues you are experiencing. If your problem continues then you need to examine your hardware for other issues.