My “My Passport” 500 GB external harddrive is not installing on my Mac laptop. The OS on my laptop is up to date. I bought the drive used on eBay. The model is WDBAAB5000ACH-00
Have you tried using the drive on a different PC? If yes and stills the same. test the unit if possible using the Drive utilities.
Also might be that the previews owner of the drive changed the file system of the drive and it needs to be formatted in order to use it on the Mac.
See if the following link helps