I have a similar problem: the screen goes white while I am playing movies on the computer, but at other times as well. If I close the lid and and allow the laptop to hibernate and then start it up again, things work OK again. But I am beginning to feel as though the problem is happening more and more often, and unfortunately, I have no idea how to fix it. I've messed with the video settings and tried various other things, but no luck: five minutes into a movie, I get a white screen and have to go through the hibernate business to get my movie back (the audio continues after the screen goes white).
I would add after some more hours trying to figure out what might be done that when I turned off the wi-fi, the computer was able to go a whole day without a white screen. I haven't been able to test it any longer than that, but when I turned the wi-fi back on after a day, it didn't take too long for the white screen to show up. Again, I haven't had the time to keep the machine on for days on end to check this out for sure, but I do know that in this one instance, I had no problems with the screen when the wi-fi was off.