External Drive not mounting on MacBook Pro Retina

Hi, you can still run Disk Utility's First Aid on your unmounted drive. To do so, select your drive from the Disk Utility left corner and press First-Aid. Wait for the process completion and the Disk utility will let you know if your drive needs repair or formatting. P.S. backup your data and then erase the drive with MacOS Journaled.

Bonjour,

Cela m'est arrivé! Essayez d'abord de le connecter à un PC Windows. Voir s'il est reconnu dans l'utilitaire de disque de Windows. Si c'est le cas, reformatez le disque dans exFAT, puis reconnectez-le à votre Mac qui devrait le réparer.

Hello,

It happened to me! Firstly try to connect it to a Windows PC. See if it's recognized within windows disk utility. If it is, re-format the drive in exFAT, then reconnect it to your Mac that should fix it.

Hello. I'm not sure if I can help, but here was my situation. For some unknown reason my WD 1TB suddenly stopped "mounting." I'm using MacOS version 10.13.4 (High Sierra). I found one of my older forensic applications called Disk Arbitrator. The application recognized my WD 1TB external hard drive as "unmounted" and I was able to "mount" the drive using this application and I was able to subsequently make a copy of the drive (data) using a software copy program and then "restore" my original drive from the backed-up drive using the "restore" function in Apple's Disk Utility application. The Disk Arbitrator program was an older version (v0.2); I could not figure out this process using "newer" version of this program. BTW, because my drive would not mount on my iMac or MacBook Pro, Apple Tech reached the conclusion that the drive had to be bad and unfortunately I was going to loose all my data. Anyway, this worked for me and I hope it may help someone else.