Once more my MacBook Pro does not recognize external hard disk
I had this problem a while ago and thought it was sorted but it's back.
MacBook Pro Retina
Question marked as
Have you restarted your Mac?
Are you connecting the drive directly to the Mac? A lot of times USB hubs and adapters are of poor quality and keep an external drive from working. If you are connecting the drive directly to the Mac, then try using a good quality powered USB3 hub to connect the drive as the hub may be able to provide more power to the external drive.
Also disconnect all other external devices to see if they are interfering with your external drive.
Do not connect an external drive to your monitor or keyboard ports as many of them are unable to handle an external drive.
@John Galt is correct that you may also have a defective cable or a failing drive.
