benny.c, yes, I've had this happen to me and it seems like it is USB specific. Are you on any network that includes even one PC, Ethernet ...even wireless? Do you have an AirPort card installed?
Although
rare in Mac computers (unless they have
Virtual PC installed, especially the new MS version), it is
especially commom on a
PC running Windows 95. Thank heaven for a MacBuddy, Aaron, that I
iChatAV with in UK (near London), he had the same problem on his CUBE. (He is on a wireless cable network with his employer - SKY NEWS)
Originally thought to have been caused by a deadly computer virus developed by some mad Belgian (Flemish) software design student caught by INTERPOL hiding in the Italian Alps, it is called
"assassino degli azionamenti duri" (non-fatal on Macs) the condition actually has a technical name in Latin:
Discus Fantasmus; or in
Italian:
Malattia fantasma del disco, as recently reported in a European technical publications through Agenzia Giornalistica Italia (AGI).
http://www.agi.it/news.pl?doc=200403151020-1020-RT1-CRO-0-PC91
I assume the drive you have is fast USB 2.0 and that it does not have a FireWire port. Correct?
Making
physical changes to the USB connection/system is what does it for me. Change ports, front, back, 1, 2, turn the cable around, switch ports with your USB mouse or keyboard, etc. If you have a USB 2.0 hub, check the power connection, and check its source cable downline.
Be sure to let us know what you have done that results in a resolution or cure for
Malattia fantasma del disco
Besides looking for the USB Drive in System Profiler,
1. open System Preferences > Startup Disk (just to see if it is there or not).
2. open Disk Utility and run
Repair Disk Permissions on "Macintosh HD" or whatever you have named your OS X primary drive
3. open Disk Utility and run
Repair Disk on the external USB Drive, if you can see it listed.
While physically checking all your USB connections,
The following is an authorized
Apple Support instructional video:
which may help put you in the mood for "success"; power of positive thinking, and all that you know.