Evidently the mac address on one of our computers changed, can some one tell what could of caused that to happen? Thanks

@rdowell 

If your device is connecting through a range extender where as before it wasn't that would affect your IP address reservation.  Range extenders will add the header for the Range Extender to your device, effectivly changing the MAC address.  

Thanks, but that is not the case. I think I might have re-installed win10, would that have done?

No, it shouldn't have.