Windows 10 install - key never asked for.

NavyLCDR said:

What you were mistaken about, spapakons, is Windows 10 checking anywhere, including the bios / motherboard, for previous operating system Product Keys. It doesn't do that. At all. At any stage of installing or upgrading. It does probably check for a Windows 10 Product Key stored in bios - but if it doesn't find a Windows 10 Product Key, it completely ignores any and all other Product Keys.

That doesn't change the fact that you can do a clean installation, skip entering a key and then activate by phone. You have to tell Microsoft that you have a genuine earlier version, so you are entitled to get Windows 10 for free. When skipping the key, there is a risk installing the wrong version (eg Pro while your previous version was Home) and then not being able to activate it. Assuming one knows what he is doing and choses the correct version, he can then call Microsoft and activate by phone. The representative will ask for proof that he has a genuine previous version, hence the need for the earlier key I mentioned.

And that would be correct; IF the Microsoft rep is willing to do it. Most of the times in the past they have told the customer to go back and install their previous OS and upgrade from it.

That's a risk to take, but a clean installation is no trouble done again, except for time consuming. You don't have to backup anything, just format and do it. So if you are lucky enough and Microsoft activates your installation by phone, then OK. Otherwise you will have to devote a couple of hours to install Windows 8.1 first and then 10. C' est la vie, as French say, or $h1t happens, as English say.