As Softspra points out, a replacement with the device manufacturer's recommended replacement part is OK but replacement with a retail upgrade part is not as far as retaining the old license is concerned. Go to Settings/Update and Security/Activation and click the link that takes you to the Store so you can purchase a license. Your new motherboard needs to be licensed.
When you change the motherboard you also change the unique IDs, hence loss of the old license.
Your license is tied to the unique IDs of the motherboard (digital licensing).
