My friend lost his Xp CD and I am reinstalling his OS XP Home addition from different Cd, and After I formatted and proceeded with Installation, now I am getting the Product Key is invalid. eventhough I have verified few times I am entring the correct product Key ( its on the side of his box) I am still getting this product key is invalid, and I am Not sure what to do at this point I cannot undo what I havd done so far and I cannot proceed , please help