1, Open a command prompt with elevated rights
* Hover mouse in the bottom left hand corner to get the start icon or use ctrl+esc or windows key / command key.
* Right click anywhere on blank space in the start launch or ctrl+tab.
* From the Apps launch start typing “CMD” then right click or arrow key til highlighted and alt+spacebar to get the options to run as administrator.
2, Type the following command to register key
Type:
“slmgr.vbs /ipk {product key, including dashes}”
hit enter
Below is a Video showing you what you need to do: