I had the same problem with my WD My Passport Ultra 1 TB HDD. I was moving a file into the drive and the device hung. I cancelled the move and, thereafter, I lost the drive. I rebooted my PC and plugged in my drive. The light the drive was flashing, but I cannot see my drive in the Windows Explorer. I panicked and went looking for a solution and came upon this thread. I experienced what the other people here were experiencing and decided to work it out myself when no one here had the solution to the problem. Good news. I got lucky.
My best guess was that the drive was still working because of the flashing light, but it was running very slow because of a file system error. I decided to wait it out until I see the drive in the Windows Explorer. A hour later, a drive icon pops up in the Windows Explorer, but with no information about the drive. The drive was assigned a drive letter, but it had no name or size. I clicked the drive icon and I get to see the drive’s directory. I could start copying my files to another drive at this point, but, since the drive was running very slow, I decided against it. But if you have a critical file that you need to get back, do copy it now. The recovery process that will follow next will not guarantee success or that that file will still be viable. Remember it will be slow and may look as if the process hung. You need to be patient. Do write anything into the drive! It could worsen the problem.
Now, on to the recovery process. Go back to drive icon in the Windows Explorer. Right-click on the icon and click Properties > Tools > Check Now. Check the 2 boxes in the Check Now window and click Start. Again, this will be a slow process and will take some time. Mine took 3 days to finish. You need to be patient and leave the PC alone to finish the job. And as I said before, I got lucky. I have my drive and files back!
I hope you have the same luck!