The community is also a great place to check out. Try these places for help from other users:
Please review the Third-Party Game Support topic to determine whether your question should be directed to the game developer or to Steam Support. Sending a support request to the wrong party may result in a delay in processing your request.
Retail CD-Keys for this game cannot be registered through Steam. If you wish to create a shortcut to this game under your Library, instructions can be found here:
Listed below are some of the errors you may experience while trying to launch Call of Duty 4.
According to Activision, this error primarily affects Windows Vista machines. Below are two solutions from Activision and Infinity Ward, respectively:
Activision FAQ for users with a RealTek sound card.
Some users with Athlon XP processors are running into issues with the latest Miles sound file being incompatible. You may still be able to play the game by copying the following file into your Miles directory and replacing the newer mssmp3.asi with the following older mssmp3.asi used in older games such as Call of Duty 2.
Note: Please only overwrite this file if you are using the XP version of the Athlon processor. This does not apply to the 64-bit version.
Extract this mssmp3.asi file to the following folder:
C:\Program Files\Steam\steamapps\common\call of duty 4\miles
You will be prompted that this file already exists and asked if you want to replace it. Choose "overwrite" or "replace".
Please follow these directions:
This error happens when you attempt to launch the game without all of the content downloaded. If you are receiving this error and Steam reports that the game's status as "Ready to Play," try validating your game cache files.
Right click Call of Duty 4: Modern Warfare > Click Properties > Click "Local Files" tab > Click "Verify Integrity of game cache"
Once the verification is complete Steam may download missing game content. When it reports 100% again you should be able to play.
Customers have reported that their Call of Duty 4 mutliplayer rank was reset after a game update on Steam. To prevent this from occurring, back up your multiplayer rank data file mpdata that is located in the following directory:
C:\Program Files\Steam\steamapps\common\call of duty 4\players\profiles\( Player Name )\
If your rank is reset, restore the backup file by copying it to the directory mentioned above and overwrite the file there.
Please see the PunkBuster FAQ for more information.