I have a Maxtor 160GB 3.5" drive in a USB/Firewire external case
(chipset Prolific 3507). When I try to use Norton Disk Doctor on it,
the test stalls at 43% complete, every time. I tried Check Disk on it
and that also stalls, both in Windows and upon reboot before Windows
loads. It's exactly the same with Win2K on my desktop and WinXP Home
on my laptop.

I tried updating the Prolific controller firmware but that makes no
difference, as does going back to older firmware.

The disk seems to work fine. I downloaded Seatools for Windows and it
checks out OK with that. What's going on?