My Book Essential 3TB Not in Finder

BAreEhD wrote:

Hi John, thanks for your reply. Since my original post I did indeed check it with another computer that hasn’t yet upgraded and it did work.

Good.

This means the drive is still functional and the problem is with the new OS.

As you might now, when a new OS is released we need to wait for updates so our current devices can work with the new technology.

This appears to be the case on this one.