I really needed a clean Windows installation, so after moving a lot of files I reinstalled it, and all went well so far. But then Windows 8 told me it wasn’t activated. I tried entering my key again, but it then told me: The Software Licensing Service determined that this specified product key can only be used for upgrading, not for clean installs. Luckily, I wasn’t the only one with this issue. This post in the Microsoft forums describes the solution quite well. Here’s a step-by-step tutorial for you. Press 🪟 to open the start menu, type in regedit and press ENTER .