I'm running XP SP2, and the drive is a 500GB My Book. It doesn't show up on Disc Management, any windows or drop-down menus, and Add Hardware and removing and replacing the USB cable have no effect (the USB port is fine; the modem works). I'd turn the drive itself off and restart it, but it's busy (even when the computer is off) and I don't know if what it's doing should be interrupted. It's been constantly whirring for at least the last two hours (when I first noticed this; it had been on a lot longer judging by the warmth), making that little Doing Stuff noise at regular intervals. It's thinking about something. Cogitating.
Planning. Its power button stares unblinkingly across the room like the world's smallest Eye Of Sauron.

Has it cut itself off from the world in order to secretly plot my untimely demise?