I’ve recently installed Windows 10 on my laptop. It was a clean install, not an upgrade from an earlier version. After installation I wanted to make sure that product activation was successful, but I found out that it failed.
Disconnect your device from all network connections and restart it. It is very important to boot the device offline, so that Windows will not try to auto-activate.
Login to your device, make sure you are disconnected and working “offline”. Open command prompt as an administrator, and type the following command: slmgr /ipk XXXXX-XXXXX-XXXXX-XXXXX-XXXXX (your product key).
If you typed in the correct product key, the following message will appear
Connect your device to the network and reboot it. After reboot, Windows will be activated.