Kerry
Thanks for your suggestion.
However, I have just realized that the problem was with the usb card
which I only installed last week. All my other stuff is hooked up to
the older usb card and only the usb HDD to the new one. So I didn't
notice initially that it was the new card which wasn't functioning.
For some reason, the SP2 install seems to have corrupted the drivers
for the new card. However, this was easy to rectify just by
re-installing the drivers.
Cheers
Paul