This is bad news, but you may be able to recover it. It is possible your external drive controller is bad. Try taking the hard drive out and plug it into your computer via the hard drive connectors in the case (if you are using a PC and not a laptop) Try to access it this way.
You could also try connecting it into other USB ports. Sometimes this is all you need to do.
If both the options above are no go, then you may try something a bit more advanced. Windows is terrible at repairing hard drive issues and reading hard drives that are somewhat "messed up". If you download a linux distro ISO to your PC and burn it to disk, you can try accessing the removable from there and repairing it or if accessible
, copy all the data off onto another drive. Download ubuntu
and burn the ISO with a program such as imgburn
. Reboot your PC and select the CD to boot instead of the
hard drive. Once Ubuntu loads, press try now, which will allow you to go into Linux
without installing it. Now connect your external drive and see if it pops up.
If it does, you are in luck and should be able to click into its file system
and copy your important files to your PC hard drive or to another external
drive. I have had personal luck with this when memory cards, SD cards, and
external drives gave errors on windows and were inaccessible. I was able to
copy the data using ubuntu. If none of the suggestions work, you may have a head crash or board crash in the hard drive itself. This can be unrecoverable, but if it is you will have to take your chances by sending it to a hard drive data recovery service center and be prepaired to pay $300-$1000 to extract the data.