I have had similar probelms in the past, Soem of the following you may have tried,
Firstly, disable your on board video
Then check your Nvidia drivers are up to date, remove your Nvidia video card using control panel system hardware options, then reinstall using up to date drivers.
Lastly if that does not work, use your Vista disk and boot up on it and use the 'Repair' option after you have told Vista your Keyboard and Language settings. This is the fix that worked for me.
Good luck
Robin
Firstly, disable your on board video
Then check your Nvidia drivers are up to date, remove your Nvidia video card using control panel system hardware options, then reinstall using up to date drivers.
Lastly if that does not work, use your Vista disk and boot up on it and use the 'Repair' option after you have told Vista your Keyboard and Language settings. This is the fix that worked for me.
Good luck
Robin