Have you tried plugging in the external first than booting the PC?
If that works, I would say your system is set up as IDE, which isn't designed for "hot swap" functions.
that doesnt make sense. with a usb hard drive its not ESATA.
If it doesnt work on any computer I'd say the power supply is going
that seems to be popular if you google it.
It should be detected and just work with vista.
step one try it on another computer
step two, try unplugging and plugging in the power supply from wall while the druve us plugged into computer.