PC does not recognize both of my 2 - My Book Essentials (2TB) at same time

I just bought a second MBE (2TB). The pc prompts for PW but does not show the drive, IF my other MBE is also plugged in. What could be up. I have run 2 MBE’s in the past. C

It’s a Windows thing probably a quick fix is simply assign one a different drive letter and put it online in Disk Manager. A permanent fix is explained here 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.