I have a Western Digital 160 GB External USB 2.0 HDD (Model #
WD1600B008-RNN). It was working well and good and suddenly it stopped
working when I wasnt around. My brother was using it and he says he may
have changed the polarity for the DC input. I had a DC adapter which
can accomodate multiple heads. I changed it to right polarity and
switched it on.

When I switch it on, both the green and red lights are always lit, PC
identifies that there is a USB device connected, but it cannot "see"
the Ext HDD. Windows Drive Information did not list this drive.

I tried with WD Data Lifeguard Diagnostic for Windows program that lets
the PC to identify the drives but the drive did not show up. I tested
the input power cable and it is working.

I suspect there is a board failure as the DC polarity was mixed up.
Since I dont work much on storage hardware, I suspect that there should
be a control mechanism/fise which may prevent the board/hard drive from
being fried.

So what would be the next logical step for trouble shooting ??

I really appreciate your help on this!

Thanks very much!!