Unplayable

[str1990]

I can't play it anymore... I got to the room where you get chased by 2 zombies and you have to get a strange green thing from a big glass container. I have no ida how i managed to get there with this framerate that i started getting. Now it is just like i am looking at screenshots that are changing every 2 seconds. I can't do anything. I restarted, closed everything (including Explorer) and tried it but it was the same . I didn't have problems with Overture, the demo of Black Plague and the begining of the full game. I have a good computer with 1GB RAM, 256Mb and 3gHZ processor. I play Quake4 without any problems but i can't play Penumbra: Black Plague .
Please help me.

Edit: I also tried turning everything (graphics mostly) to minimum.