I have two USB external HDDs on my Windows XP SP3 system. From time to time, one of the two drives (always the same one) doesn't display (show up) in "My Computer" even though it seems to have loaded properly at startup and is functioning. Usually after one or two reboots, it finally displays properly..
That happens here also, more often after computer goes to sleep. The way I wake the USB drive up is to
- use the safely remove hardware option, wait till the light goes out, then unplug the usb cable
- unplug the power, make sure it stops spinning,
Then plug the power cord back, then the USB cable. Never failed yet. Bit easier than restarting the whole computer, maybe.
Edit, after Alan's post while I was typing. My USB HD has always done that, since it was new. But lately it is making disturbing noises, so I backed up the whole drive to another one.