Windows 10: Can't find old Windows activation key

Hello, I purchased a Windows activation code from the Microsoft store back in 2019 to use on a PC I had built. I returned the PC shortly after and I was told that the activation key would be linked to my Microsoft account. I have since built a new PC and I cannot find the activation key anywhere in my account or emails. Can someone tell me how I can find the key?

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Windows 10 will not activate Error code 0x803F7001

thanks
I activated my Windows 10 from product key Windows 7

 

activate windows 7 oem key

There is no difference between the OEM disc and the Retail disc with Windows 7. A retail disc will accept a OEM or Retail key, and vise versa.

If the OEM Key wasn't going to work with the disc you have, it would have stopped you during the install when it first asked you for the key, not during activation.

What is likely the problem is that, since the OEM version has already been activated once, it is failing activation again. Activate it over the phone using the option given to you on the failed activation screen, and you shouldn't have a problem activating it.

 

Windows 10 Pro Activation Key

I have lost access to Windows activation key following motherboard failure. Due to age of laptop, I have replaced it and now wish to upgrade Windows Home to Pro on the new one.

The activation Key does not appear to be linked to my microsoft account although the old laptop is still in list of devices and confirms professional version of Windows had been in use. The hard drive from old laptop is functional and i wonder if there
is any way of retrieving key from files.

any suggestions would be greatly appreciated.