First, try a chkdsk /f on the drive in question and see if that helps, there might be some bad spots.
A friend has an issue, where the drive was said to be "RAW". This is what I did to fix it:
* I tried a chkdsk (drive letter) /f and got an indication that the disk was a RAW disk.
* In Windows Explorer it said it was an NTFS disk.
* When trying a CD to a folder, it said nothing was there.
* When trying to access the folder in Windows Explorer, it said nothing was there.
* Windows Explorer said that "X" was used out of "Y" space
* This fixed it:
* * * Unplugged from his USB Hub
* * * Unplugged the hard drive from the power source
* * * Waited a short time (about 1-2 minutes)
* * * Powered drive on (not plugged into the computer)
* * * Plugged in to USB hub
* * * All fine.
Last year, or late 2012, I had an external start to act flaky, and had issues getting to it (it wasn't like the "RAW" issue above). So I downloaded UBUNTU (UBUNTU.COM), burned a DVD, and booted it as a LIVE DVD. A live DVD is running UBUNTU from DVD, not the hard drive. In the live DVD, you have a file manager, like Windows Explorer, and you can access external drives and partitions, thus you can copy the files off, possibly.
I was able to get 98% of my files back. Windows wasn't able to read the external, but UBUNTU (LINUX) was able to. You'll need a partition or another external drive that you can copy the files to.
If any other members have suggestions, it would also be good to hear.
Best of luck.