The Dell Windows CD is original, of course, and I can provide all the necessary documentation, otherwise I wouldn't be asking support here. So far I never had to use the Windows XP CD that I received when I purchased a Dell Dimension 4500 desktop PC years ago. Now that I had to substitute the hard disk, when I try to install XP on it, it asks me for the product key. I use the Product Key Number in the Microsoft Certificate of Authenticity sticked on my PC, but the installation first asks for it, and then doesn't accept it and stops. What am I supposed to do now?