I'm having the same issue wtih a Nvidia gforce 4 mx 420. I think it may be related to the power mangement because when I press the power button that starts the shut down process I can see a screen for a few moments unitil the power is killed. My screen isn't exactly blank as it is not even on as if there is no power from the video card, but it only happens after when X runs. I'm not a linux expert, so I don't know how to fix this, but thought I would add additional info.