WD Passport keeps unmounting

By disconnecting, restarting Mac, and reconnecting the WD HD, it will show up in Disk Utility and I can partition it, but it later unmounts and I have to repeat the process.  Meanwhile it’s not backing up my Mac Hd.  Ideas? Thanks.

Sorry, it’s a WD My Book and my computer is a Mac 10.6.8.

what type of Mac?

could be a power issue or the cable is faulty

It’s a Macbook.  I’ve used 2 different cables.  The light is on as if it is receiving power. I downloaded a software update and it seemed to work, and I reformatted it.  For awhile it seemed to be backing up my Mac HD, but then it disappeared.

You will need to replace if this is the case