Modern Warfare 2 Aiming help?

Ok so last night I was playing MW2 at my friends house and I was doing really good every single game. My friends connection is extremely good like four bars but mine is always three. I am now at my house playing on a new tv, controller, connection, etc. and I am doing really horrible every game. It is extremely hard for me to aim for some reason. I was wondering is there was anything I can change besides sensitivity, like the horizon or verticle margin or anything that will improve my aiming just like it was at my friends house. Thanks in advance!