|A power surge or power spike event can damage anything that was connected to the mboard when that event happened. That's even more likely if the event was caused by a lightning strike. |
That having been said, there may be nothing wrong with the external enclosure's circuits or the hard drive inside of it - in that case, something else is not right that is causing it's partition(s) to not appear as (a) logical drive letter(s) in My Computer (or in Computer in Vista or Windows 7) .
(NOTE that Vista's and Windows 7's NTFS version is slightly different than the version used in 2000 and XP. If (a) NTFS partition(s) was (were) made on the external drive in Vista or Windows 7, 2000 and XP cannot recognize that NTFS version and will NOT show that (those) partition(s) in My Computer. Vista and Windows 7 will show a NTFS partition that was made in 2000 or XP fine in Computer.)
If the external enclosure's circuits are damaged, it can be replaced cheaply, and it's a lot less likely that the hard drive inside the enclosure was damaged.
Troubleshooting USB device problems including for flash drives, external drives, memory cards.
See Response 1:
Check that out first.
Rarely, not all the ports on the back of a desktop case may be able to supply 500ma each.
If you have a desktop computer, Note that I answered a Topic on this site where a guy had an external drive, which does require the full 500ma, connected to a port on the back of a desktop case - it would not work properly when a webcam was in the port next to it, but it worked fine when the webcam was unplugged. Ports on the back of a desktop case often have two ports connected to the same USB controller module that are ports one above the other - you could try connecting the cable to one of those and leaving the other un-used.