Click Multiplayer Options and make sure PunkBuster is enabled. Title: CoD4 PB Files - Windows : Game: PC: UNKNOWN GAME: Origin: EU: Filename: File 6409 - gaacod4win32.zip: Sizes: 4.3MB (Download): Hits: 3,285 Downloads. Now load up COD4 multiplayer and go to options on the main menu. Now right click 'PnkBstrA' again and click Restart. Change the startup type to Automatic then click Apply and OK. Scroll down to the one named 'PnkBstrA' and right click it and choose properties. Go to start, control panel, administrative tools, then open services. It'll do a check of the files then you'll get a pop up. Now redownload the PunkBuster setup file from here and run it, follow what it says on the screen (select install/reinstall). Far more than a list of species and their status, it is a powerful tool to inform and catalyze action for biodiversity conservation and policy change, critical. When it's downloaded move all the files into the PB folder in your COD4 directory (if you got COD4 from steam it should be c:/programfiles/steam/SteamApps/common/Call of Duty 4) This will start downloading the PunkBuster files you need. Frequent cheat updates, ensuring your favorite cheats are promptly updated for new game versions when needed. Get powerful, private cheat features like our deadly bone aimbots, 3D ESP, and exclusive features like our Warframe damage multiplier hack. Go here (You might need to register), and click the top link for 'windows-file94'. Supporting 20+ private cheats that you can start dominating with in a matter of minutes.

In case you didn't get it fixed, i had the same problem and solved it by doing this.

Pb update cod 4