I'm chiming in here with a similar problem.
My trusty My Book 250 MB has worked perfectly from plug in +3 yrs ago until today.
I noticed it was strangely quiet, then saw it wasn't listed on My Computer directory. It still has it's glowing green circle but is otherwise lifeless.
XP Pro SP3, using USB 2 port.
All connections are solid.
I don't see it in the Device Manager, at least that I recognize. There are five functional USB controllers, some IDE ATA controllers but I think that is for the hardwired drive.
I ran the WinDlg.exe diagnostics but it doesn't see the My Book.
Since it's been so trouble-free I don't have the moves down for troubleshooting.
It hasn't made any unusual noises and was involved in my automated backup last night.
I think it predates the SmartWare software. I don't find it installed and it can without a disk.
What are the troubleshooting steps?
If it is dead is there any way to grab the contents? It was my backup.