|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 recently 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.
If you are CERTAIN all of those possibilities don't apply, you could test the hard drive, but Toshiba does not have hard drive diagnostics for their drives.
Seagate's harddrive diagnostics will test any brand of hard drive but can only attempt to fix Seagate or Maxtor drives (by filling the drive with zeros which wipes all the data), and only the Windows version of it can test hard drives when they're installed in an external enclosure - you would need to test the external drive when it's connected to another computer (and it's being recognized by the mboard's bios, or course).