Cannot see TWO drives simultaneously (4TB USB 3.0 My Book Essential); only one at a time

WD External Drives External Drives for PC
1

TWO drives (My Book Esssntial, 4TB, USB 3.0) are plugged into a new Dell Optiplex, running Windows 7 Professional.  If both drives are plugged in and turned on, I can only see ONE in My Computer.  One at a time, there is no problem.  Why can I not see both drives simultaneously?

I also have two drives made by Buffalo Tech and I do NOT have this problem.  Thinking this might be a bus power problem, I turn off both the Buffalo drives, but can still only see one WD drive.

2

I had the same issue … you have to (with Windows 7) go into disk management and enable the second WD drive. 

3

It sounds like a Windows Disk Signature problem. See if this helps fix the problem   http://community.wdc.com/t5/My-Passport-for-PC/Copy-files-from-one-drive-to-another/m-p/277504/highlight/false#M7587 see post 11.

Joe