civ 5 won't start, says unknown error, steam support as helpful as a sack of bricks

hello everyone, so when i double clicked civ 5, it said it wa supdating, but 2 seconds later it said preparing to launch civ 5, i waited a minute, and then it said unknown error.
i tryed steam support, no help.

civ 5 has always run fine, well, as fine on having to play the game on directx 9 with everything lowest quality, fully zoomed in, with strategic view on, but i digress...

my question is does anybody have any idea what the heck to day, i REALLY want to finish playing my first immortal difficulty game (i'm 5 turns from diplomatic victory as indonesia, why you have to not let me play civ 5 :cry:)