After videos and mp3s play well on your computer but not when played from the HDD, then most probably the problem is caused by the USB cable or the HDD itself.
You can start with testing the drive with the tool that I already provided. It will show you whether there are some bad sectors on the drive.
Faulty cable, could cause file corruption as well. So, you will need to try connecting the drive with another cable.
If the test results show that the HDD is fine and the cable isn't the issue, I would advise you to back up the data and format the drive. You can write zeros as well(there is an option of it in WD's DLG tool).
Hope this will help,
D_Know_WD