Welcome to the community, subu444!
Well, @13thmonkey is right. The NTFS is a file system which can easily get corrupted (into a RAW unformatted drive) by improper connection to a device or without safely removing it as one. In general, in order to be able to change a file system you'd need to format the HDD. You could try using third-party software apps to retrieve your files, but I guess that's at your own risk. Here's a discussion from the TH community that could give you some ideas though:
http://www.tomshardware.co.uk/forum/280932-32-hard-drive-recovery
I'd also recommend you to use your HDD manufacturer's diagnostic tool to check up on the drive's heath and SMART data status. You should be able to find such a utility on their website.
Good luck! Hope this helps you!
SuperSoph_WD