Hello,
Since you mentioned the drive got disconnected while in use and now it is not seen on the computer then it means the partition is corrupted. I recommend that you try to use the “drive repair” option in “disk utility”.
http://support.apple.com/kb/ht1782
If this does not work then you can always format your drive in order to use it again. Please note that formatting the drive will delete all data stored on it.
How to partition and format a WD drive on Windows (8, 7, Vista, XP) and Mac OSX
