@Manojkhedar No you don't need to buy another licence. It depends how the system is licensed:
- Firmware embedded key (most modern computers from large companies such as HP, Lenovo, Dell etc) - it should just re-activate when you've re-installed Windows
- Subscription or other digital key: It should just re-activate when you add your licensed account to Windows
- Product key: You'll need to enter your product key to re-activate, this is most likely on a sticker on the case.
