I have problems playing dirt 2 on pc?

ever since i bought dirt 2 about a month ago it hasnt worked. and ive tried everything i know how to do it still wont work. what happens is i go to play the game it loads up and after the opening credits and once you get to the main menu nothing happens just blank screen. i have tried finding contact numbers for steam and code masters and i can find any. dirt 2 demo worked fine. i have uninstalled dirt 2 and reinstalled it (via steam download). and every time i try to play nothing happens and its just that game that does not work. please help. and all of my computer drivers are up to date including the graphics card that is up to date. and still does not want to get past the menu screen and i can still do stuff in the game with the keyboard but i cant see what im doing its just a blank screen. please help me thank you is in advance