Hey there again, @AnoopNair!
I'm glad you managed to retrieve your files from the WD External drive! The best way to avoid data loss scares is to always backup your files to multiple storage locations/drives. Always remember that "backup" means that you have your data stored in at least two (2) locations. Moving data from your system drive to an external hard drive or another internal HDD is not a backup, unless there is already a duplicate of the file on a different drive off-site as well as on-site.
That's the best tip I can give you to avoid these issues in the future.