If you see a screen asking for a "CD Key" on the original COD4, hit Cancel . You don't need it anymore. Just set your name and join a server.
If you want to play Call of Duty 4: Modern Warfare online, you might be confused. The original game is old (released in 2007), and its old "GameSpy" account system was shut down years ago. easy account cod4
So, how do you get an "account" today? It depends on you are using. If you see a screen asking for a