My computer is running the Windows 7 operating system with 4 GB RAM and Corei7 processor. I have been facing many problems in this particular operating system, ever since I have installed it. The new situation that has encountered my system is that Fable: The Lost chapters is not installing on Windows 7. This is a game that I bought recently and when the installation wizard asked for the serial key, I entered. I received an error message soon that "This is invalid". I am not able to understand whether the system is prompting me about the key or the game. Kindly provide some help.