Welcome, Deepu_1!
@popatim is right, you should check the external HDD manufacturer's official website for any software utilities for your model that compatible with this Window OS version. Either way, make sure you backup all the data from the drive on the Windows 7 computer and make sure it's safe and sound elsewhere before proceeding with the troubleshooting.
You might also want to
uninstall & reinstall it as a device from Device Manager. Hopefully, this could also help with the proper detection of the drive.
Keep us posted & good luck!
SuperSoph_WD