Last year I upgraded my Windows 8.1 license to Windows 10 via the free upgrade programme.

Yesterday I needed to reinstall Windows 10. I booted into the USB to install and I entered my Windows 8.1 product key, and it says my key is not accepted.

This is on exactly the same hardware with no changes whatsoever.

EDIT Downloading and using the latest Windows 10 ISO and signing in using my Live account solved the problem.

  • 1
    While linking with your Microsoft account solved your problem, I wonder how this is solved for people who don't sign in with a Microsoft account. – adampski Sep 27 '16 at 11:01
  • Well, I'm guessing it just pulled the product key from my account online. I bet had I not had a Live account it would have let me enter the key manually. – Chad Johnson Sep 27 '16 at 11:15
  • Seems like typical Micrsooft to essentially force you to log in with your Microsoft account again to license Windows. I can't see why it would be so complicated to put a flag on the product key their end to 1) prevent confusion and 2) allow install without signing back in with Microsoft account. – adampski Sep 27 '16 at 11:24

You do not need a product key to reinstall Windows 10 on an upgraded device. You have a digital license which will be activated online after installation. Skip the step that asks you to enter the product key.

How you activate Windows 10 after reinstalling it depends on how Windows 10 was originally installed on your device.

If you activated a free upgrade to Windows 10 or bought and activated Windows 10 from the Windows Store, you have a digital license for your device. This means you can reinstall the same edition of Windows 10 that your device has a digital license for without entering a product key. During reinstallation, if you’re asked to enter a product key, you can skip this step. Windows 10 will automatically activate online after the installation is complete.

Source: https://support.microsoft.com/en-gb/help/12440/windows-10-activation


You need to re-install Windows 8.1 and then you'll be able to re-apply the Windows 10 upgrade.

Your Windows 8.1 key is not a valid Windows 10 key because it's a Windows 8.1 key - quite simple really :)

  • I actually tried that. I reinstalled and activated Windows 8.1, and then I tried upgrading to Windows 10 (both by running the setup while running Windows 8.1 AND by booting into the flash drive), and I get the same error about the product key being invalid for Windows 10. – Chad Johnson Sep 27 '16 at 10:11
  • You odn't use your product key for Windows 10 - at all. You install Windows 8.1 -> enter product key/activate -> install Windows 10 through the update – Kinnectus Sep 27 '16 at 11:01
  • I was actually able to do a clean Windows 10 install without having Windows 8.1 installed. I skipped entering the key, used the latest ISO, signed in using my Live account, and Windows was activated automatically. – Chad Johnson Sep 27 '16 at 11:14

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