on the contrary Spoony, if the new board had a different chipset the copy of windows will likely be unstable on the new build (though there are rare occasions where it will work).
Just copy all your files to another HDD or flash drive, nuke the system drive, reinstall, and copy the files back. Obviously this will not work with programs.
You can move your OEM win7 to another machine. When I did my recent upgrade it never even asked me to call in and change things. But if it does you can explain your situation to the fine people at MS and they will transfer the license to the new machine for ya.
Your copy of Windows is locked to the PC on which you purchased it. You cannot transfer that license to another PC.
You can upgrade any components or peripherals on your PC and keep your license intact. You can replace the motherboard with an identical model or an equivalent model from the OEM if it fails. However, if you personally replace or upgrade the motherboard, your OEM Windows license is null and void.