Some people like me wants to install a fresh installation of Windows 8 without having Windows 7 pre installed. It’s faster and probably cleaner too. The only problem is that the early Windows 8 Pro Keys were Update Keys so they can’t be used for a full installation. After searching at Google I found a way to tell Windows that is was installed through the update process and finally activate my key :
slmgr /rearmand reboot with
slui.exe 3and enter your key
If the last step doesn’t work, reboot and try the last command again.