Hi aruna dalai,
Since the external keyboard works normally, please try one additional check that hasn't been mentioned yet:
- Restart the laptop and enter its BIOS/UEFI setup using the key specified by your laptop manufacturer.
- Once there, check whether the built-in keyboard responds, for example by using the arrow keys.
- If the keyboard also does not respond outside Windows, I recommend contacting the laptop manufacturer for further hardware diagnostics.
If it works normally in BIOS/UEFI but stops responding after Windows starts, please let us know. That would help narrow the troubleshooting toward Windows or the keyboard driver.
I hope this helps identify where the problem is coming from.