Sorry for posting in this old topic, but have to express thanks for all the excellent knowledge to be found on this forum (just spend a little time searching).
Problem like the OP, in one of my laptops, an external usb HD did not show up (but was listed in Devices & Printers...). Then found this:
Have you tried assigning the drive a letter in Disk Management?
Try adding the drive letter in Disk Management
Fixed! (just the remaining question as to why it was not automatically assigned a letter, like it used to).
Anyway, thanks a lot.