Multi Player Help Easy Thnaks

Ok , So i bough COD4 For my PC and I passed The Missions Now And I wanted to play multi player on my PC but when i press Join A game It Doesn't Show Any Games Its blank. Also I tried Joining a Game through xfire my friend was on playing and i press join game then it said error different server something like that. I haven't played it yet i just got it 2 days ago please help.

Try to download the latest patch

download the patches (1.4 , 1.5 , 1.6 , 1.7) And then play

& make sure that u have key code or buy it or play in private servers ..
should work