Windows 10: Windows product key won't activate - Limit Reached

HiI have a product key I purchased for windows 7 Pro back in 2010. I've been a Mac user for many years since then and have recently returned to Windows. I built a new PC and did a clean install of windows 10 using my existing product key, which worked perfectly. I then decided to upgrade the motherboard and do a another clean install, when I went to re-activate Windows 10 using the same key, it wouldn't work. I went into my Microsoft account and deleted the old PC on the other motherboard that was using the key and tried again, still no luck. I went through the troubleshooting step

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Windows 10 product keys and activation - and the KMS angle

Changing the product key to the generic Windows 10 product key will reset activation to the standard retail channel for activation. It might just activate (if there was a previous digital license for Windows 10 for that computer established with Microsoft). Once Windows 10 is back on the retail activation channel, then more than likely changing the product key to the Windows 8 product key using the same method may work.

 

Windows 10 will not activate Error code 0x803F7001

thanks
I activated my Windows 10 from product key Windows 7

 

Activate windows 10 after re-installing (I have lost my product key)

I own a Lenovo T430 laptop. In 2017, I installed Windows 10 using my original Windows 7 product key. Unfortunately, I cannot find that product key anymore. I need to re-install windows 10. Will it be automatically activated after the installation, if I skip the step of asking the product key during the installation?

In my opinion, I believe that my laptop will have a digital entitlement stored on the Microsoft Activation Servers and this will not be a problem. Is that true?

If not, please suggest me a solution or a workaround.