I've just upgraded my activated Windows 7 Professional to Windows 10 Pro. 

I upgraded, rather than making a fresh install. 

During installation I was asked for the product key, it wasn't accepted, so I proceeded without the key. Now when I try to activate I get this error:

```
You are running Windows 10 Pro. The Product key you entered cannot be used to activate this edition.
Error Code: 0xc004f210

```

I looked into similar questions like [this](https://superuser.com/questions/1000959/unable-to-activate-windows-10-with-error-0xc004f210) and [this](https://superuser.com/questions/1072958/getting-error-code-0xc004f210-when-trying-to-activate-windows-10-with-a-windows), but the difference is that I upgraded (rather than doing a fresh install) from Win 7 professional to Win 10 pro. I don't mind reinstalling win 7 and doing it all from scratch again. But I was wondering if there was an easier way.