Cant detect one of two of my external 2TB my book essential 3.0

hi everyone, i had a problem that i cant detect one of two mybook. each of them is edentical. same type and same hard drive size, is it possible at the first place to connect both at the same time. i can only boot one external hardisk at a time. before this i tried to connect one mybook essential 2TB and another wd element 1TB and it works perfectly. 

1 mybook essential 2TB in 3.0 usb slot  + 1 mybook essential 2TB in 3.0 usb slot = both detected in “safely remove hardware and eject media pop up” but not showed in my computer. (unbrowsable) 

1 mybook essential 2TB in 2.0 usb slot + 1 mybook essential 2TB in 3.0 usb slot = both detected in “safely remove hardware and eject media pop up” but not showed in my computer. (unbrowseable)

1 mybook essential 2TB in 3.0/2.0 usb slot + 1 wd elements 1TB slot 2.0 usb = Both detected in “safely remove hardware and eject media pop up” and  showed in my computer.  (browseable) 

thanks in advance, any reply would be appreciated badly :). 

oh no. nevermind just found out how to. i just need to turn it online on disk management :)