Unrecognized USB External Drive

I have a Seagate Barracuda that froze up on me: would not spin. It was an
internal slave drive in an XP box. By tapping on the drive case I got the
drive unstuck. I installed it it in a USB external drive container after
configuring it as a master. The XP machine does not see this USB device.
I've tried various sequences of plugging in the drive and starting it and
the computer, but the computer remains oblivious to the drive. I swapped an
old 40GB drive for the Barracuda, and that drive is seen.

Can someone give me a clue as to what problem is staring at me?

Thanks.