What happens if you go to Start -> Run and type ...
explorer X:
... where X is the drive letter of your external drive?
Alternatively, go to Start -> Run and type ...
cmd
This will open a DOS window.
Now type ...
dir X:\ /s /p
The above command should list the files on your external drive.
Type Ctrl-Break or Ctrl-C to abort the listing, and type "exit" to return to the Windows GUI.