When you upgrade the motherboard, Windows recognises the computer as a different system (because it is). Depending on what key(/license) you have, it may or may not allow you to use that key.
It depends on if you have an OEM or a Retail key. With an OEM key, you can only use it on one system and that's that. But with a Retail key, as long as you completely uninstall Windows from the previous system, you're fine to use it on a new system. You occasionally need to use phone reactivation.
It depends on if you have an OEM or a Retail key. With an OEM key, you can only use it on one system and that's that. But with a Retail key, as long as you completely uninstall Windows from the previous system, you're fine to use it on a new system. You occasionally need to use phone reactivation.