Also worth a try, the user may have not done a safe remove hardware, therefore corrupting the device drivers for that device. Each usb data device has a unique serial number which is assigned to its own driver.
Plug the device in and MMC/Device manager, Under usb devices, right click and remove all storage device drivers. unplugg the device and restart the machine. Try plugging the device i again.
just another solution before you go formating the drive