

If not, although I never got around to it, I'm sure Apple Care will have some suggestons. Check back later with it's Finder window or Computer screen and with some luck, it appears! You're back in business.

(Allow some time) for the USB 3.0 External Western Digital 3TB HD, My Passport For MAC to be recognized by the computer, a laptop in my case. As some time had passed, 15 to 20 minutes, while I was discussing this issue over the phone with Apple Care, yet before we were able to implement any Apple Care solutions, I opened up the Finder window and sure enough there and on the computer screen, was the 3TB My Passport For Mac! Recap: From my experience, find a newer second computer, even a friend's, who's running the latest operating system. So here's how I was able to bring back! Since I had access to an additional computer, with the latest Operating System, Sierra 10.12.3., I plugged the USB 3.0 External Western Digital 3 TB Hard Drive, My Passport For MAC. Now, I know the 3 TB HD was running because I could feel it the rotation of the hard drive and I could see that it's exterior white light was on. There it would allow me to select Verify and Repair, but once the process ran its course, a window would pop up to say an error has occured: "Couldn't open disk" or "The disk couldn't be unmounted".

The 3 TB HD icon wouldn't show up on either the Finder window or Computer screen, on my Desktop computer, but would show up within the Desktop computer application, Disk Utility, on the left side of it's window. While running a Late 2009 Mac Desktop, with Yosemite 10.10.5, I was attemping to back up with Apple's Time Machine application my Desktop Computer onto my USB 3.0 External Western Digital 3 TB Hard Drive, My Passport For MAC. I had the same problem too, but with a USB 3.0 External Western Digital 3TB HD, My Passport For MAC.
