Asking for a friend who's just built a new computer. They had Windows 10 on their old computer (was a retail Windows 8 upgraded to Windows 10 through Microsoft's free upgrade offer) and wants to transfer their license to their new computer. They've installed Windows 10 on the new computer without a product key for now. They've always used a local account, so can't use the activation troubleshooter. And when they rang Microsoft, the call quality was bad enough that it was hard to get the the Windows 8 product key across to the call center worker, and once they had gotten the key across, the call center worker just said that the key was invalid. Any ideas on how to go about this?