My response is a little old, but you never know who it could help. I had not plugged in my hard drive for a minute and actually thought I had misplaced the AC adapter during this last international move. Somehow, when I tried to access the information on my WD external hard drive, I got a message asking me to format the drive if I wanted to use it. The drive registered, but showed 0kb, like it had spontaneously self-deleted all the files.
However, after reading everything here, and nothing worked, I decided to try a partition restoration software. It is called Active Partition Recovery out of Canada. I bought the $40 version after spending hours trying other things to scan it, etc. I could see the files. I simply right clicked on the drive to restore the boot sector and everything reappeared.
Just thought I would pass it along.