My WD drive is not showing in finder but I can see it in disk utility with a grey color I can't see my external Hard Drive in finder but i can see my hard drive in disk utility but in a grey almost transparent color. When I try to run a "first aid" this is what i get as an error: 
Running First Aid on “BENJA'S HD” (disk2s2)

Repairing file system. Volume is already unmounted. Performing fsck_exfat -y -x /dev/rdisk2s2 Checking volume. Checking main boot region. The volume  could not be verified completely. File system check exit code is 1. Restoring the original state found as unmounted. File system verify or repair failed.
Operation failed…

Any idea what I can do? thanks!
As the message said your drive is connected but it's not mounted. I recommend the 3rd party app Mountain which gives you better access to all your volumes. You can mount, unmount, and eject volumes by just clicking. The app is not free but there may be a free trail period. Using Mountain you can mount your volume. 

I am in no way affiliated with this software. I'm just a happy customer.