Settings:
all settings works from low to high, but texture detail should be set less than HIGH.
I got the minimum settings:
core i3 3.07GHz
win8 64bit
GeForce GTS 250, 1GB (i think greater than the GeForce 8600 or ATI Radeon HD 3600)
RAM 4GB
First solution: re-install the game.. it worked.. but the next day, it went back.. i dont remember if i changed the settings or not..