Hi there Vishvas Arora,
One thing you can try is to attach the drive with a different USB cable to another computer. That way, you will rule out a possible connection related problem.
In case the issue persists, then there's something wrong with the enclosure or the HDD inside has failed.
What do you mean by "understood the problem"? Did you send out the drive to a data recovery company? If the data is really important, you will need to use the services of a data recovery company. Just check a different one.
If the drive is under warranty and you don't really need the data, you can just contact the place you got it from and RMA it.
Let me know in case you have some more questions,
D_Know_WD