Mac book with new motherboard not connecting to mybooklive-backup

Hi, When I try to access the mybooklive-backup drive,  it says connection failed (via time machine or finder) it says I need a registered username and password, which does not corespond to my WD registration.  I can access the public files on themybooklive drive. WD say it is a TM problem, Apple say it is a WD problem. I have files in there but cannot access them.  How can I figure this out? Thanks

In Time Machine just connect as Guest. That should work. If you have created private users, this would be when you would need to put in user authentication.

Unfortunately I tried that and it said An unexpected error occurred (error code -6584)   I don’t seem to be able to “turn on”  the backup drive for either my computer  to recognize it.