Windows 10: Unable to reactivate Windows 10 pro on secondhand computer after reinstalling Windows

Hi all,I recently purchased a computer secondhand, which came with Windows 10 pro installed. I had problems resetting the computer I think because the restore options weren't set up by the previous owner, so I had to use the Windows installation media to reinstall Windows 10 from a USB drive.Unfortunately, it now won't activate the Windows account. It's showing as Windows 10 Home edition and it's not signed in under my Microsoft account. I followed instructions online to retrieve the activation code from the computer registry - and this has given me a code - but when I try and enter this pro

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Trying to reinstall Windows 7 Home premium from Windows 8 Pro

Hi, I have just installed Windows 8 pro and I don't like it. I tried it for a day but I think it has too many unnecessary functions, which drives me crazy. I tried to re-boot with Windows 7 disc in it, but I am unable to select anything using keyboard and mouse on windows 7 installation step (where i choose language and input). Please help.

 

Motherboard change unable to reactivate Windows 10 Pro -

I have searched this topic and everything seems to be almost a year old. This is a homebuilt machine circa 2015. It started with an ASUS FM2+ motherboard with an AMD A5600K processor. It was Windows 7 Pro, upgraded to Windows 8.1 Pro then to Windows 10 Pro.
Saturday the motherboard died. An exact replacement could not be located so a Gigabyte card was installed. No changes to the hard drives. Booted the machine and Windows automatically started and then did a "revert" then installed the latest updates. C Drive was in the red so I deleted all of the old install files using Windows Clean-up. Went to reactivate, checked the significant hardware change and entered my MS account information - The computer (none of my computers) were listed and now it is telling me that I have to spend $200 to buy a copy of Windows 10 Pro.
Have not yet called Customer Support as the computer is at home and I work during the day -
I do have a disk image or two that may be a year old -

Suggestions - should I just shell out the $200 and move on

TIA

 

Motherboard change unable to reactivate Windows 10 Pro -

Activate using windows 7 pro key.