Hey there, Rahul.
Have you checked if the drive is recognized by Disk Management as well? Would you please be so kind as to post a screenshot from what you see there (you can use imgur.com to upload the image)? Here's how to access it:
How to access Disk Management in Windows to manage hard drives.
Try the drive with a different USB cable (since you are using it with an external enclosure), to see if the same thing happens. While we're at it, go ahead and try it out with a different computer as well, either by connecting it with a different enclosure ro by going directly for a SATA connection.
If none of that helps, you could try accessing the drive via Ubuntu Live USB/DVD, to see if it's properly recognized and if you can get to your files. Another options would be to go for data recovery software as a possible solution:
http://www.tomshardware.co.uk/forum/id-1644496/lost-data-recovery.html & http://pcsupport.about.com/od/filerecovery/tp/free-file-recovery-programs.htm.
Hope that helps. Please let me know how everything goes.
Boogieman_WD