Hi
was the Windows 7 DVD a:- retail / retail upgrade / system builder or OEM recovery disk
The first two will allow re activation after motherboard change the second two will not
(unless you can convince Microsoft that the motherboard died and that model is no longer available)
Windows 7 will probably reboot OK but it would have helped if you prepared in advance by un-installing drivers for sound, network card, Hard disk controller etc before final shutdown on old motherboard
[and copying drivers for new motherboard onto hard disk]
best of luck
Mike Barnes