it may sound silly. But I had the same problem once, I could not retrieve anydata from the Hard Drive. I put it into the freezer for the night, as a friend told me, and in the morning I could access to the hard drive and save everything on another hdd.
I don't want you to destroy a hard drive if you find any other solution. However, it worked for me.. I dared to try only because I did not know what else I could do.