Windows 10: I bought windows OS and have product key, but cannot activate it on my computer, Why?

I bought windows OS and have product key, but cannot activate it on my computer, Why?

:)

 

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 product keys and activation - and the KMS angle

My ASUS Laptop that I bought years ago has an embedded key for Windows 8 (Core). What I got on a clean install of Windows 10 was Windows 10 Home. It activated just fine and got a Digital License for Windows 10 Home. The sticker just Said Microsoft Windows 8, no product code was listed anywhere on the PC.

 

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.