To clean install Windows 10, you need more than the product key from an upgraded instance of Windows 7/8. You'll need a file called tokens.dat created during the upgrade process.

Here's what happened to me:

  • With Windows 7 Ultimate installed, I started the upgrade process to Windows 10.
  • Once that was done, I used Nirsoft ProduKey to get the Windows 10 product key.
  • Then I formatted the hard disk...
  • And tried a clean install using the Windows 10 install DVD.
  • When prompted, I used the product key I got previously from the upgrade.
  • After a few days of successfully using this install, Windows 10 was suddenly no longer activated.
  • When I re-entered the product key, I got error 0xC004C003 that activation failed...

I think this is the problem - on a formatted hard disk, Windows does not know that it was an upgrade, and the product key (which is valid only for an upgrade) will fail activation! In my case, this activation error was delayed by days.

I did a bit of research, e.g. How to rebuild the Tokens.dat file when you troubleshoot Windows activation issues - Microsoft Support and repeated the install Windows 7 - upgrade to Windows 10 - format - re-install Windows 10 process a couple of times.

I think Windows 10 knows it's an upgrade from the tokens.dat file. So, simply backup this file, do the clean install, and re-copy it!

To get to the file from the command prompt:

  • From the start menu, type cmd but don't press enter.
  • Right click on Command Prompt and select Run as Administrator.
  • From the command prompt change to this directory.
  • And copy the file to a USB thumb drive, e.g. G:
    cd %windir%\ServiceProfiles\LocalService\AppData\Local\Microsoft\WSLicense
    xcopy tokens.dat G:

Run Command Prompt As Administrator

If you don't run cmd with elevated administration privileges, you'll get an Access is denied trying to change to that directory.

That worked for me, and it's been over a month now... Now I not only keep a note of my Windows product keys but also backup tokens.dat.

As a final side note, for those with a copy of Windows 7 Professional/Ultimate lying around (again, not an OEM but a retail license), but are using Windows 8/8.1, I'd recommend you "downgrade" to Windows 7 Pro/Ultimate first, then upgrade to Windows 10, because that'll give you Windows 10 Pro. Specifically, according to Microsoft's Upgrade to Windows 10: FAQ:

Windows 7 Edition Windows 8.1 Edition Upgraded Windows 10 Edition
7 Starter
7 Home Basic
7 Home Premium
8.1 10 Home
7 Professional
7 Ultimate
8.1 Pro
8.1 Pro for Students
10 Pro

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