Video slows way down at a specific point

[PLEASE HELP]

So after i solved the demon dogs puzzle, i used the keycard to access the research room via the card scanner. Immidiately upon entering the room the game runs unplayably laggy. In example; it will take 10 seconds for the screen to redraw from a mouse movement, the audio also repeats in the way old games like CSS would do when a server changes a level. This will not resolve itself!

Anyways i have an AMD A6 APU with ATI video , all new drivers, 64 bit windows 7 and the game has run perfectly until i entered this room. I have the updated version of this game.....I cant continue! What gives.