Windows 10: After OS Fail & Reinstall my Win 10 Pro Product Key Does Not Work

My ZTSystems pc, purchased in 2010, originally came with Win 7 Home. Later in 2010 I purchased from Amazon Order #105-7252976-4066631 a Win 7 Pro upgrade Microsoft Windows 7 Anytime Upgrade [Home Premium to Professional] from MS but no longer have that info. A few months ago I replaced the HDD boot drive with a Samsung 870 EVO 1 TB SSD. OS migration went great. Then I purchased a Win 10 Pro DVD from a reseller and successfully installed it over Win 7 Pro. PC has worked great ever since. The SSD made a big improvement in performance. A few days ago something, I don't know what, happe

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How to get product key of old OS (Win 7) after upgrading to Win 10?


OK guys, this will take time, encoding in process but after that I need to do some basic editing and add explaining titles before I can post the video:




The process as I did it:

• Install Windows 8.1 Pro on a new machine, activate with a valid product key which had never been used before. A totally virgin key. Activation OK
• Reinstall 8.1 Pro on same machine wiping the HDD, use the same key to activate. Activation OK
• Reinstall 8.1 Pro on a new machine, use the same key to activate. Activation OK
• Upgrade the last install to Windows 10. Windows 10 activation OK
• Reinstall 8.1 Pro on a new machine trying to use the same retail product key, resulting this:

 

Why was I not asked for a product key when upgrading to Win 10?

According to your spec you have Win 10 Pro, but perhaps that doesn't reflect your PC.

You haven't stated which edition of Win 10 you have on this machine, nor what your Win 10 key is for.

For example, if you already have Win 10 Pro and your key is Win 10 Home, that would be a retrograde step.

For interest only:
Change Product Key in Windows 10

More on product key if you search this list or look at 'Related Tutorials' in the above.
Windows 10 Tutorial Index

 

Win 10 Pro upgrade using Win 8 Pro product key

I just bought a new computer running Win 10 Home. When I went to upgrade to Win 10 Pro using my Win 8 Pro product key from my old computer, the upgrade wouldn't activate.

Now I'm stuck with a bunch of error messages (mainly 0xC004C003) and am being told windows isn't activated. I can't seem to get my activated Win 10 Home back.

I don't have a product key for the Win 10 Home because it came pre-installed. There's no product code recorded on the packaging or labelling on the device.

So:

How do I either

• activate the Win Pro upgrade, or
• Get my activated Win 10 home back?