2nd WD My Book Essential

I just bought another WD My Book Essential and it will not recognize in my computer when the first one is plugged in, I looked under “Manager”, the computer can see it. I also opened the WD utility and it sees the drive but wont give it a letter.

I tried switching USB ports, changing the drive letter(upon restart my first drive changed its letter) I still cannot see the 2nd drive when the first one is present and vise versa. 

Any help on this matter would be great.

Side note, is there a power adapter that will work with these in Germany?

Maybe this will help. http://community.wdc.com/t5/My-Book-for-PC/when-I-connect-two-quot-My-Book-Essential-quot-drives-only-1-is/m-p/49988/highlight/true#M2419