Activate Windows

1. Open Settings > System > Activation.
2. If it says Windows is activated with a digital license, you are done. Signing in with the Microsoft account linked to that license helps reactivation after a hardware change.
3. If Windows is not activated, select Troubleshoot. When you have changed hardware, choose I changed hardware on this device recently and pick the device tied to your account.
4. If you have a product key, choose Change product key and enter the 25-character key.

A watermark that says Activate Windows does not block security updates. Buy a license from Microsoft or the PC maker rather than a random key from a listing site.