I have a WD My Passport external USB3 drive, that connect to the Mac with a USB3–to–USB cable. I tried a different (known to be working) cable and both USB ports.
My laptop crashed one day, and ever since, I cannot mount that drive. Another WDMP mounts without a problem on the same Mac.
I can mount the drive in question on another Mac, and under Linux.
When I pull up console, I see no activity when the drive is attached.
This is a MacBook Pro (early 2008) running El Capitan.
Any thoughts on what I can look for to resolve this?