I tried to activate my Windows 8 Enterprise, and to my surprise I can't find a way to enter the product key. I later found this method to be useful. First open the command prompt. To do so, press Windows + r key and type cmd and press enter, or just press Windows key and type command prompt and hit it. Now type the following command and press enter: SLUI.EXE 3 Now you will see a window prompting you to enter the key. Enter the key and press activate. Bingo...