I am experiencing this problem with several HP scanners on Windows 7 in our Organization.
If the technician or the user mistakenly connected the scanner to the machine before installing the drivers, the scanner won't work. Sometimes the scanner is found the device manager under "imaging devices", but the scanning software says "No scanner was found". uninstalling the driver and reinstalling it does not solve the problem.
Is there a way to solve this problem without having to reformat the machine?