WD MyBook has stopped appearing on MacBook Air

I was using the My Book yesterday to transfer files from a Mac Book Air. The Mac Book powered off before the My Book could be ejected. I have tried to access the My Book this morning from the Mac Book and it does not appear in Finder. I have tried connecting it to an iMac and still cannot get it to appear in Finder. I can see the My Book in Disk Utility, but the drive is not mounted. Grateful for any assistance.

Hi @SaulFowler
Have you opened a Support Case? If not opened, for more information, please contact the WD Technical Support team for the best assistance and troubleshooting: