Quick question. If I build a new PC and move the hard drive from my old unit to the new one, will the activation code still be valid? Isn't it based on the computer's configuration (MB, CPU, etc)?
If the license was not purchased through a retail store, such as through the Microsoft store app then it's not a product key. These types of licenses are called digital licenses and are are associated to your device based on a hardware profile. To reactivate after a significant hardware change. https://support.microsoft.com/en-us/help/20530/windows-10-reactivating-after-hardware-change
You will probably have call Microsoft and explain to them that you got a knew motherboard and it is not activating. If that is the case they will give you a new key to activate it. I had that problem when I changed out motherboards in mine.
Sonny is correct. After a hard drive or motherboard change, you have to call Microsoft and they will give you a new key. There is a limit to how many hardware changes to a computer. Many years ago, l had a desktop computer and changed the hardware many times and they said l was over the limit and ended up going to a computer store and plunked down 300 dollars for a new windows 7 professional disk with key.
Just a follow-up... If I swapped my current system drive to my new PC, will it check and change the system drivers automatically or must I do a clean install of windows 10, and reinstall all my other applications again?
I built the new PC and moved the ssd from my old system to the new. Windows 10 started right away unactivated as expected, but I was able to activate it again (online) without a hitch. I then updated with new MB drivers. Works great!