Portal 2 keeps crashing?!

[C0SMYK]

Portal has always worked fine before, and when I'm able to get to the main menu, but when I start to play a chamber (whether its co-op, single player, or a community chamber), the game crashes as soon as it stops loading. I have no clue whats going on. Any help?

P.S. I run a 64-bit Windows 7.

[_I_]

verify game cache

from your library, right click on portal 2 -> properties
local files tab -> [verify intergrity of game cache..] button

if it still crashes, update or roll back your video drivers