ok, so we now can say that the disk per se, is fine. The problem looks to be on the desktop itself, which is useful to know.
It doesn't much like your USB ports does it? If you are looking at a hub or similar, might I suggest a PCI USB 2.0 card? You can get them much cheaper these days than of old. That would provide you with four USB 2.0 ports (Some have firewire on the same card too) that will be as useful as they are cheap. (PM me for sources if it helps)
The reason that I say this, is that I would now suspect your existing USB sockets on the desktop. A new PCI USB 2.0 card will plug into a card slot and be powered from the existing bus and provide plenty of "Oomph"
Just a final thought - the device manager on the desktop has no problems showing with the existing USB layout?
Conan