I bought this drive of off ebay ( model # wd50000h1cs-00) Came with power adaptor. I plugged it in, white bar lights up on front of unit. Plugged in USB cable to my Windows 7 machine, and the OS is not picking up the drive. Then tried on another PC, same issue. I see there is some sort of power button(?) on the back, but does not appear to do anything. Any clues?