Let's say you bought one of those $30 Windows upgrade promotion keys from Microsoft last year and now want to perform a clean install. What do you do?

The media you downloaded does allow you to perform the install but windows will refuse to activate a new install with that upgrade key. Unless you perform this magical process.

If you don't know what you are doing, stop and call a friend. If you make a mistake with regedit, you can harm your windows installation.

• Start Regedit
• Navigate to this registry folder HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/CurrentVersion/Setup/OOBE/
• Double click on the MediaBootInstall key and change the value from 1 to 0
• Open a cmd prompt with admin rights and execute this command: slmgr /rearm
• Now you have to reboot Windows

You will now be able to activate your windows with that upgrade key you bought.