Hi,
it looks like a graphic issue.
Well your image you uploaded is not really that good to be sure.
Seem you set the wrong resolution or other graphic settings.
End Steam and the Game, than go to your steam folder where your MW3 is.
Rename your "config_mp.cfg" file and restart the game.
It will be recreated than.
Try lower resolutions first and slowly change them to higher resolutions do it only one by one.
Also you could try to update your graphiccard driver.