I use Windows XP with my Umax Vista flatbed scanner. Photoshop sees the scanner, troubleshooting says it's working fine, it's connected, but the preview and full scan results in a solid black page. Very puzzling.
I suggest that you uninstall the scanner,reboot windows a few times without the scanner attached and only then plug it back in and install. If the scanner is ok, the drivers should reinstall correctly. Also go to umax website to see wether there are any newer drivers, that should do the trick.