Hi atul.koundal,
I hope you are doing well. Based on your post you may try the following basic troubleshooting steps.
1) Have you tried to connect the using different port available on your PC? You may try to connect the drive through another port if you have not tried.
2) Try to connect using another USB cable, sometimes the cable might be failing or not supplying enough power to the drive.
3) You may try to connect the hard drive to another system to check the hard drive is working or not?
4) Are you able to use other external drives without any issues?
Try to check in device manager with the following steps.
From the start menu right click on the Computer and choose Manage.This will bring up the Computer Management Window. Now you can see Device manager on the left hand side under the heading System Tools.
In Device Manager, double click to expand "Universal Serial Bus controllers", Check if at all there is an exclamation mark along, the driver, it suggests issues with the driver installed. Right click on the "Uninstall" and click "OK". Then try to reconnect the drive it should show up.
If it doesn't appear in Device Manager then you could try checking in Disk Management. Check if it appears there, sometimes it may turn up as Disk 1 or Disk 2, and the status. You could try to initialize and format it from here.
How to partition and format a WD drive on Windows (8, 7, Vista, XP) and Mac OSX .
To make sure if there is any damage on the hard drive you may run the Data Lifeguard Diagnostics from WD. Below is the link with guidelines.
How to test a drive for problems using Data Lifeguard Diagnostics for Windows
I hope it will help you.