With your product key in hand, ready to Activate your newly installed and running Windows 8 system, you head on into the control panel. In the Windows Activation screen it tells you that it can’t activate right now. Your reaction is what???? or WTF, whatever your lingo may be. No problem, just do this.
Open a cmd prompt and run as Administrator. Type in the following:
An application pops up, you enter the product key and you are activated. Don’t ask me why, it just works. You may find a better way, but you can run with this one now if you want.
Thanks to http://www.windows7hacker.com/index.php/2012/08/how-to-change-windows-8-product-key-to-complete-activation/ , with appreciation.