Using a Windows 8 upgrade key for a clean install

I recently faced reinstalling a Windows 8 machine, without knowing the key used for deployment on it was an upgrade key. Not wanting to wipe the drive (again), dig up a Windows 7 key, then installing Windows 8 again, I googled and found this advice at Lifehacker, which worked brilliantly:

If you do a clean install using the Windows 8 Upgrade Assistant, you should be fine, but if you’ve already formatted your drive or you’re moving to a new drive, you can’t do a “clean install” without installing an old version of Windows first. It’ll let you install Windows 8 cleanly, but when you go to activate, you get an error 0x8007007B, saying your product key can only be used for upgrading.

If you get that error, here’s how to fix it:

  1. Press the Windows key and type regedit. Press enter to open the Registry Editor.
  2. Navigate to HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/CurrentVersion/Setup/OOBE/ and double-click on the MediabootInstall key in the right pane.
  3. Change the key’s value from 1 to 0.
  4. Exit the Registry Editor, press the Windows key again, and type cmd. Right-click on the Command Prompt icon and run it as an administrator.
  5. Type slmgr /rearm and press Enter.
  6. Reboot Windows.

When you get back into Windows, you should be able to run the Activation utility and activate Windows as normal, without getting an error. Obviously, you could use this trick for evil, but it has its legitimate place too—if, say, you’re upgrading your hard drive and want to do a fresh install on it, or if you formatted your drive before upgrading.

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