I have a Windows 7 Pro pc and Epson Perfection 1650 scanner. I've been running the scanner on an old W XP machine for years because the software that came with it wouldn't run on W Vista on my new machine. I upgraded to W 7 Pro and could use the scanner software bundled with W 7.
I disconnected everything to take my pc apart and clean it. I plugged everything back in and for some reason the computer won't detect the scanner. I rebooted it, re-downloaded the twain software from Epson - which it said it successfully installed, and the computer makes the usb sound when I unplug it and plug it back in.