My Book Essential not connecting to my MacBook Pro

My, My Book Essential Eddition is not connecting to my MacBook Pro.  I upgraded to OSX Yosemite since I last used My Book.  I have tried on two other Mac Books with the same result.   One is still runnonmg on 

Any suggestions what I do now?

Hello,

Go to disk utility and verify if you can see the drive in there. If possible try to format it. Note that formatting the drive will delete all data stored on it.