Need a better description of the problem to properly diagnose, however the most probable problem is punkbuster. http://www.evenbalance.com/ get it here.

Hello everyone,

I have joined steam since March this year, and I am wanting to make new friends and also need help in improving my skills in Call Of Duty Modern Warfare Multiplayer.

I have an 1.5 Version of the game. I have been playing for a year and still do not see any improvement in my skills so I am looking for pros and also advanced players to be friends with and play a good match and learn at the same time.Also having a Steam account I have no idea how to use Steam by making new friends and adding my non Steam call of duty multiplayer to the application, I am using Mac to let everyone know.

So hopefully I could make new friends on here and meet Call Of Duty Modern Warfare Multiplayer players and learn well from them on improving my skills in the game.

Thank You and have a nice day.