Amneisa: The Dark Descent Problems[Help?]

[Spawnehh]

Well, I just recently bought Amneisa; The Dark Descent, and I have it's demo aswell [Windows]. I have tested the Demo but won't work normally. For example; I start the demo, it begins, Daniel says his lines but the screen is black. Once everything is done and you hear the water flow, all I can see is a white little box in the middle of the screen. I move the mouse and sometimes I spot the hand and click, it is for a door. Still my screen is black [Expect for the white box, of course]. But then again, it is currently FULLY black now.

And this is the same problem for the original game. Nothing. Works. I Honestly don't know what to do, I know it's a GREAT game, but this is a horrible problem I can't figure out since I'm not that much of a computer person. Also, is it normal for when you launch the game you are not able to control your mouse as it goes to the top left corner of your screen?
Could any of you help me?