Welcome to HP Forums @Debargha,
Thanks for the post.
I understand that the wireless mouse is working and the keyboard is not working after replacing the batteries.
Not to worry, I will be glad to help.
Have you tried any troubleshooting steps on your own?
Recommend you try the steps suggested under "Wireless mouse or keyboard does not work" section in this HP Article.
If the issue persists, please contact our phone support for the service options available.
Let me know how it goes.
Chimney_83
I am an HP Employee