hi, i have ATI graphics card HD 4850, now i can't see the physics in Brother's in Arms:HH. please help me.

First I would update the drivers for both the video and sound card. Since the sound card works in tandem with the video card its drivers are necessary as well.
Also you should go into the video card settings and lower or disable the options including anisotropic filtering and antialiasing. If it works then start enabling the video options one by one to find the one that is causing the issue.