It happens to all of us. For some reason you need to reinstall or upgrade your Microsoft Windows installation, but you can’t find the installation CD. The good news, you can reinstall Windows without your original CD. The bad news, you’ll need your unique activation code, which is usually written on the lost CD’s case.
Hopefully you have your product key saved in a safe place and can find it. If not, and your computer is still usable, you can use Magical Jelly Bean Keyfinder [1]to find your product key. Once you know your product key, you can use any Windows CD (of the same version of course) to reinstall or upgrade your computer. When prompted, use YOUR product key to activate the Windows installation.
PS: If you bought your computer from a major manufacture, the product key is often attached to the computer case as a sticker.