In this video I use slui 3 and slmgr.vbs -ipk [product key] to change the product key of Windows 8. Once you enter a valid product key you can activate your operating system. If you use slmgr.vbs to change the product key, you can also use slmgr.vbs -ato to run the activation after the product key is entered. Be sure to run the cmd as an administrator.