Tried deleting and reinstalling the 3100cn drivers. Rebooted. Windows still does not see the USB printer.
I deleted the drivers again. I also used regedit to delete all instances of "3100cn" in the registry. Strangely, Windows would not allow me to delete two keys but all others were deleted.
Reinstalled driver (printer not plugged in of course). Windows still does not see the printer. I tried multiple USB ports but it makes no difference. Windows will not recognize and install the printer.