Windows 10: My computer died, I got the product key from it. How do I reuse it?

A week ago my computer was acting up and I thought it would be a good idea to get the product key from the computer and so I did by using this tutorial below. A few days ago my computer died on me. Instead of buying a new computer I wanted I decided to build one and I have put Windows 10 on it. How do I use the product key from my old computer and use it on the new one I built? I want to have a offline account and I did have an offline account on my old computer which was not attached to any Microsoft email.

Find Windows Product Key using CMD or PowerShell

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reusing my product key

If I purchase windows 10 License key now and I upgrade on the PC I'm using now. If I go buy a new PC a week from now am I able to reuse my windows 10 product key on the new PC I purchased????

 

Reusing windows 10 retail product key from broken pc

Soon after windows 8 first came out I downloaded it and purchased the product key which I used to upgrade from windows XP. There was a special offer at the time which meant it cost only about £15.00 but it is a genuine retail key not OEM. I later upgraded
to windows 10 using that product key. After some months the computer, which was really quite old, broke down completely. I now have a new windows 10 computer. However this only has windows 10 home installed and the key for the old computer is the pro version.
I have read that you can deactivate a product key on one machine and reuse it on a new one. However, as the old computer does not work I cannot do this. Is there any other way to deactivate and reuse the old product key on my new computer?

 

Reusing W10 Home product key after upgrading to W10 Pro


A long time ago I upgraded a computer from W10 Home to W10 Pro. This was a custom build and both the original W10 Home activation and the new W10 Pro activation were done via product keys ordered from Amazon.

No Microsoft account has ever been involved with either key. Back in May of this year I completely reinstalled Windows but I don't really recall if I had to reactivate the license or not.

And now I'm wondering if I could reuse the original W10 Home product key on another computer, and if it would affect the current W10 Pro activation in any way. Would the original Home product key still be tied to my main computer's motherboard or did that history get wiped when I upgraded to Pro?