external USB HDD not working

[TCav]

One of the things that happens is that, if the drive hasn't spun up, it won't respond to handshaking requests from the computer's USB controller. As it happens, whena hard disk drive is first powered on, it draws the most current. If the external power supply is only just enough to run the drive, or if the driveis old or already has other problems, the drive may take longer to start up and may be more likely to time-out the USB interface. And if the USB hard disk drive is connected through one or more USB hubs, the likelyhood of this occuring mayincrease.