michaelH1958,
Questions:
TheThe sys in question, the one with the new motherboard, it was a name brand? Asus? I mean before the motherboard change?
It had come to you (you purchased it) with Windows 8/8.1 pre-installed?
If so - your situation is fairly cut and dry, hasn't changed since Windows XP days at least: you had an OEM license. That OEM license *is* tied to the first computer it was installed and activated upon. While people have argued (philosophically) when a
computer is no longer the same computer when you change out parts - it was defined by Microsoft at one point as "the motherboard" and, in modern times, (the last 18 years or so), given how much is contained in the "motherboard", that makes perfect sense.
If you changed your motherboard thru the manufacturer under warranty, your manufacturer should have made you whole in terms of the operating system they shipped the system with. That is part of the OEM agreement they make with Microsoft.
If you actually have a retail copy (directly supported by Microsoft) of Windows: you are responsible for keeping up with the product key (with 8.1 and prior.). You lose that, you lose the rights to utilize Windows.
As far as Windows 10 being ''full of bugs", while I would say there are issues with Windows 10 and, in my opinion, 8.1 is likely still the most stable currently suppprted Microsoft OS out (yep, I liked 7, 8.1 was/is more stable and does run better, IMO)...
I wouldn't say Windows 10's issues center around "bugs" as much as usually a lack effort (which, it may be a bit much to expect effort in this manner) from the end-consumer in terms of device drivers and configuration of their settings (don't just accept defaults
anymore.)