Remove the disk from the USB case and connect it directly to a PC. Then run hddreg on it, which can revive bad disks and doesn't harm it.
http://www.dposoft.net/After that use the fujitsu diagnostic utility to scan the HD, which can repair further issues, and after that again use getdataback on it if the data still can't be accessed directly. But if possible don't use it in the USB case, as that can add extra issues. The diagnostic tools of all HD manufacturer's are on the UBCD.
http://ultimatebootcd.com