1) MOVE all files to another drive then read them again. If still corrupted then DELETE them. (I'm not sure if you can even move corrupted files).
2) Now run a complete diagnostic (likely DESTRUCTIVE) which is why I recommended moving the files. Diagnostics are from the Manufacturer and a full diagnostic takes many hours (perhaps 10 for a 2TB drive).
3) If it PASSES, then do a FULL FORMAT on the drive (will take hours to complete). This will build a bad sector table to help avoid future corruption. (If it FAILS, return to Manufacturer if under Warranty. If NOT under Warranty throw it out.)
4) If it Passes and the FULL FORMAT is completed, move back the files you copied.
*It's also important to note that the PROBLEM in an external drive may NOT be in the hard drive component but rather in the electronic circuit board.
If the diagnostic reads "FAIL" and the external drive is ALSO no longer under Warranty then I suggest you crack open the case, hook up the drive internally in your PC and run the diagnostics again.
(My Western Digital Elite drive failed so I cracked open the case and hooked up the hard drive to my PC using the SATA power and data cables. It works fine now.)