WD Duo - does not start after plugged in wrong power cable

Hello,
I hope there are some ideas out there what I could do. I have a WD Duo which I used as one drive.
I have accidently plugged-in a wrong power cable and since then the drive does not appear on my PC. When I plug it in (with the correct power cable) the fan starts up and runs for 2-3 seconds but then stops and nothing is happening on my PC (i.e. no drive is shown in “MyComputer”). The fan also doesn’t start again, but there is the light on.
I have bought a new case and put the drives there, but with the same result.
Does anybody have an idea what I can still do?
Thanks a lot in advance for your help
Michael