OSX El Capitan / Not Recognizing USB Hard Drive I updated to OSX El Capitan a few weeks ago, and ever since I did so, my computer is having some issues with my Seagate USB 3.0 hard drive.

In terminal, when I use the disk utility, the drive shows up, but it generally will not mount.  I say generally, because occasionally the drive will mount, but it is unusable (Time Machine and disk utility give me issues). 

I have tried reformatting the drive with no luck - the disk utility says that it cannot unmount the drive.

Any thoughts?  Happy to take screen shots if needed.
I have a Seagate external drive and found that the NTFS for Mac OS X had to be removed and reinstalled. (Apple logo / Preferences / NTFS for Mac OS X - right click and remove)  This link will take you to the free update.  It worked for my Seagate drive but no my Octigen one.
http://www.seagate.com/gb/en/support/downloads/item/ntfs-driver-for-mac-os-master-dl/