Windows licenses usually have no restriction or link to your hardware.
I have reused same Win 7 OEM license on about 50 PC's and never had an issue. (after 3 times you will need to ring MS to activate)
My current Win 8.1 enterprise has been on about 10 different PC's and i had no issues with activation.
With windows 8, some manufacturers embed the license in to bios so you might want to run belarc advisor to get all your licenses backed up.
Ah cool, I thought new MOBO meant new Windows 7!? So not? How can I find out if it is tied to the MOBO/Bios? Will you get issues if you update BIOS also?