Vista - Dual Monitor Problem

I had a problem with my dual monitors last month and Michael Solomon
suggested that I uninstall the video driver and then install the latest
drivers for my nVidia 7900 GeForce GS. I did this and then both monitors
worked fine and the display properties control panel listed 2 monitors
again. But after several days,the left monitor stopped working and the
display properties reverted back to 1 display only. So I uninstalled and
then reinstalled the latest driver and both monitors worked and the display
panel showed the correct number of monitors until this morning. Now I'm
back to only one monitor working and the display properties panel is showing
only 1 connected monitor.



My OS is VISTA Home Premium.



Does anyone know why this is happening and what I can do about it?



Thanks.