Hi there, I recently upgraded a friend's computer to Windows 10 however I didn't do it through the normal OS way, and now the windows is not activated. I can't go back to the old OS, however I do have the product key that was on his laptop on the old OS, but this does not work if I put it into Windows 10. Does anyone know what I can do?
You probably did not upgrade to the same version/edition of Windows 10. A few things will tell you what went wrong.
First, run Showkey Plus from this forum. In the upper right corner is an option to check product key. Enter the old product key there. When you get the results, you can click on the product key to blank it out on the screen, then post the results here.
Showkey - Windows 10 Forums
Second. Run winver (either click start icon and type winver - or win key + r and run winver). Post results here.
Finally, open command prompt (admin) [found on right clicking start icon]. In the command prompt window run:
slmgr /dlv
Post the results here. There is no uniquely identifying information in the results, so you don't need to edit anything.
We should be able to tell you exactly what mistake was made from those results.
Quote