Hello doleary477,
Retail purchases of the Office H&S 2007 product include one license; this license permits up to three simultaneous activations on computers used by members of the same household where the use is in non-revenue generating activity.
If you have a retail license for Office H&S 2007, you are permitted to move the installation(s) from computer to computer, as long as you do not have the product activated on more that three computers at any one time. In your case there won't be
an issue, just replace the motherboard and most likely since it is identical to original you won't even have to reactivate Office. (Depending upon circumstances you'll probably have to reactivate Windows.)
There is no publically-accessible Microsoft utility that keeps track of how many activations have been done with any give Office product key.
