|"Shut everything down for the night and now I can't get access to it again". |
Did you simply shutdown the computer, or disable the USB device first? If you write to the USB drive and then immediately shutdown, the drive may not have finished writing before power was interrupted. While it isn't necessary to disable any external drive prior to shutting off your computer it is a good idea to give the drive a little time. Windows is supposed to prevent this behavior from happening. If the drive is corrupted that would be the most logical reason why.