A Windows 10 digital license is associated with your PC hardware. We do not have OEM stickers or product cards. To see the full key, you need to use a third party program such as ‘Product KeyFinder’. If your Windows is unactivated, please use the ‘Activation Troubleshooter’ in Windows.
Please note that you will have to add the device to your Microsoft Live account to transfer the key after you change motherboards. You can do this by going to Settings > Update & Security > Activation > Add a Microsoft account.