I had the same problem when I installed Windows 7. I have an Acer x243w (primary) and a Viewsonic vx2025wm (secondary) and the vx2025 was not recognized by Windows 7. Opened NVIDIA Control Panel and tried to get it to detect the second monitor (several times) with no luck. I reinstalled everything (viewsonic drivers
, Nvidia control-THEN Windows 7) to no avail.
I finally powered off my pc, disconnected the DVI cable to the vx2025, then the power cable...powered on my pc, only the x243w was still seen and powered off. Connected the DVI & power cables to the vx2025 and powered it on-then powered on the pc, went to the NVIDIA Control Panel and it detected it-FINALLY!
Yesterday, I tried opening Outlook 2007 and it said I needed to update Windows Connector-I declined and it wouldn't get any new email in Outlook. I closed it, and like a fool, I tried to do the upgrade. I rebooted and the mobo put the boot screen and data on the vx2025, as usual, but when Windows 7 booted the vx2025 disappeared! I then did a system restore from a few days ago and everything came back fine...ran virus, malware, etc. scans without any major issues. Ran registry cleaner and all is back to normal (whatever that means).