Do you have any sort of volume manager or partition manager software installed? Or something else trying to take control of the usb drive that could be crashing?
If you have no joy with anything else then before trying a re-install you could try Start.... Run...then type "sfc /scannow" (without the quotes) and press OK. This is the System File Checker and might help.
Or if it was working before you could do System Restore possibly?
