Weird Textures in Penumbra Overature

[amnesiauser9392]

I have a Radeon ATI 4600 HD graphics card with the latest drivers and windows XP 32 bit operating system. I have amnesia and it works perfectly with all the highest settings When I play Penumbra, the textures of the crates are half filled in and sometimes when I enter different areas the walls are see-through. This really takes away the horror factor of the game. Not to mention the most annoying thing when I press ESC, the game freezes. I should be able to play this game fine! (I have everything on the highest graphics settings e.g. motionblur, trilinear, etc.)

Please help!