There was a power cut. W7 took about 20 minutes to repair itself, but in comparison that was just a minor inconvenience.
The working usb HD is dead. The pilot light doesn't light up even. I've tried different usb ports, but no, it remains dead, and I've not backed up on to the second, older usb drive, (still working), since before Christmas. One bit of luck is that the RAWs from my latest session with Axajay, 26.02.14, were still on the memory card in the camera, but I've lost all the conversions, and I can never seem to convert exactly the same a second time.
I don't fancy taking the usb drive to a data recovery specialist, because of all the confidential stuff on it, if indeed the data is still there.