Hey there, Ravi. Welcome to the community!
First I'd recommend that you try the drive with a different USB cable (not longer than 12") and a different computer to see if the drive is recognized properly. If that doesn't work, you could try accessing the drive via Linux Live CD/USB to see if you're able to get to your data this way and retrieve it. You could also try some of the data recovery options from this thread as well: http://www.tomshardware.co.uk/forum/id-1644496/lost-data-recovery.html
Hope that helps. Let me know how everything goes. Good Luck!
Boogieman_WD