@mohit29794
What you need to do, since there is nothing we can do to test your keyboard, is get an external USB keyboard and plug that in.
If that works, that shows that at least the basic system, including the motherboard, is working properly and then, most likely, the keyboard would need to be replaced.
Sorry, but this is just a self-help forum staffed mostly by volunteers and we are neither able, nor permitted, to provide any repair estimates or equipment prices.
For this information, you would need to contact an HP Repair or Service Center.
If you live in the U.S., here is a link to the HP Service Repair Centers:
https://www.service-center-locator.com/hp-hewlett-packard/hp-hewlett-packard-service-center.htm
If you live outside the U.S., here is a link to HP Service Centers, by Country/Region: https://support.hp.com/in-en/service-center
Good Luck
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