hi guys my son had w7 pro on his PC it was a student edition from digiriver, unknown to us there was an expiry date ie 2 years , my son has bought a new pc witoutany operating system and we loaded the w7 pro disk that came as part of the download as a hard copy of w7 but the product key is not liked by the system , can i get a product key from Microsoft ? how much ?, or do i have to buy another w7 pro disk to get the key ?