Windows 8 users who noticed that the operating system can’t be activated after the installation may want to try the following workaround that worked to activate when installing Windows 7 using an upgrade on a clean PC.
Open regedit by pressing Windows-q, entering regedit and selecting the result from the list of hits.
Navigate to HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/CurrentVersion/Setup/OOBE/
Change MediaBootInstall from 1 to 0
Go back to the start screen and enter cmd there.
Right-click Command Prompt and select to run it as administrator.
Type slmgr /rearm on the command line and hit enter.
Reboot Windows now.
Run the activation utility afterwards, enter your product key to activate Windows.