Demo trouble

[Alex3051]

I recently discovered the Penumbra series and really wanted to try them out, Black Plague especially. But when I downloaded the Black Plague demo download from the Frictional Games site, I encountered a problem. When I tried to play the tutorial and the game itself, I couldn't see anything but a white screen. I know there's supposed to be a contrast so you can see the ground, but this didn't happen. Nor could I see the box that drops in the tutorial for you to interact with.

The same thing happened when I downloaded the demo for Overture. The game would load up just fine, it would go through the story scenes just fine, and then....white screen. Couldn't see anything. Little icons would come up, and I could interact with an apparently locked door, but I couldn't see any of the environment. Please help! I really want to play these games