Left For Dead Freezing!! please help

so ive just bought left for dead a few days ago it runs fine ive played it quite a few times i tried to run it today and it will go through the first cut screen after loading the game and it goes to load the main menu and freezes my computer....
i dont know whats wrong and i dont know where to start i know it ran fine before the update is this only happing to me?? any advice out there???

oh yea and im running it thought steam if that helps

 

Make sure you don't have anything blocking steam, firewall, router or anything else. If you're used to running that service you probably got that set up already, right? Double-check, just to make sure no one changed the settings when you weren't looking.

Is the game fully patched? Do any other applications misbehave? More importantly, if it worked yesterday but not today, what changes, if any, have you made to your computer?

Oh, and system, specs, especially graphics card and driver would be good to have.