Call me a lucky SOB but I tried the "tapping" thing to no avail. Then I got this sudden urge to open the drive and spin the platters by hand!! I gave it a few turns, the closed it up. And it's working now!

Everything is being backed up to a firewire drive at the moment. I REALLY hate this WinXP Home "restore" feature but it will have to do for now. Is Norton Ghost the way to go?