Whenever i try to launch Left 4 dead 2, it's say's "preparing to launch left 4 dead 2" *Then doesn't launch at all when it's finished preping. I've Validated my files, reinstalled the game, even reinstalled steam. I've also defraged my files, still nothing. I've noticed with task manager that the process instantly closed, but my firewall is turned off and i'm only using Microsoft Security Essentials as an anti virus. Any help?