It's possible to recover a lost PC game's CD key by using programs or software that have been designed specifically for such tasks. A good example is the Game Key Revealer software. All product keys are stored within the registry files of a computer, and what these programs do is to search the registry files for the key that is lost or forgotten.
The first important thing is to sign in as an administrator. The Internet offers a wide range of programs to search for a game's CD key both free and paid. Download and install the key finder software following the steps on the installation wizard. It important to follow the steps correctly for the installation to be successful. The next step is to launch the software and scan the computer's registry files. Some programs need the user's input to get started. The scanning process will take several minutes depending on the amount of files to be scanned. Once scanning is complete, the software provides a search list of different registry keys. It's possible to find the key that corresponds to what you want. If the software fails to find the key, searching through the registry files using Ctrl+F to find it may be an option.