I know about updating the directx and graphic card drivers, but it couldn't be this because i have direct 11 installed on my pc and newest grahpic drivers. I tried to install new one but it didn't work. Do you have any ideas?

P.S
Here is my computer:
OS:Windows 7 Ultimate 64bit
CPU:AMD phenom 2 x4 955 Black Edition 3.2 ghz
Graphic Card:ATI HD6850 with ATI Catalyst 11.6
Directx version: 11
RAM: 2x2GB Kingston Hyper

Direct X doesn't work like you think. Its not like an application where you upgrade from one version to the next. With Direct X you can have every version of Direct X installed and it will use the version which is closest to the version which the game uses.

Basically you should try installing Direct X 9. It won't overwrite Direct X 11, you will still have Direct X 11, just means you would have both Direct X 11 and Direct X 9 available for applications to use. Certain games will not work if you don't have Direct X 9 installed.