I know how frustrating this problem can be. My screen was flickering and
shaking, showing the desktop items sometimes and sometimes not. I did
everything I could think of. (I even did a fresh reinstall of Vista to cure
the problem.)
Finally I went to Nvidia and downloaded the latest driver for my card. That
did the trick.
Make sure your cables are pluged in and tight. One loose cable can cause
the same problem.
I have a Gforce 6100 graphics card so I went to Nvidia and downloaded the
latest vista driver for that card. I was sure to TURN OFF ANTI VIRUS
PROGRAMS RUNNING IN THE BACKGROUND before installing any drivers. I did not
UNINSTALL the old drivers first. It seemed to work ok that way. I rebooted
and that is all I did.