You can never use an old OS install on a HD and move it to *new* hardware .... think about it, you boot the machine, it posts, the OS starts loading drivers for hardware that is no longer there ..... and you do not have hardware for drivers that is there..... not a good situation.
As to the validity of your license, if it is an OEM license you **may** have an issue with activation. It is oft wrongly stated that a MoBo invalidates the OEM license. This is not always the case as I have replaced any MoBos and CPus w/o issue. It's been a somewhat common activity of late in fact as users have brought back failed 1156 MoBos (2 resulting from over tightening mounting mechanisms on CPU coolers) where if ya replace the MoBo, ya need a new CPU also. By sticking with the same brand, you will likely wind up with the same or similar NICs, sound, hardware which will not trigger a *change* as far as the activation goes.
The only way to know however is to reinstall the OS...... I'd not consider a "repair" and go straight for a fresh install..... repairing won't remove all traces of the old drivers and can lead to bloat and conflicts. If you have trouble activating, call Microsoft and explain that you had a hardware failure and the new MoBo was the closest upgrade replacement available to you.