Who knows? I had a somewhat similar issue a few days ago: was playing C&C3, alt-tabbed out for a min (prev did it just fine) then when I got back in, screen was completely black even though sound worked fine. I had a black screen regardless of trying to alt-tab or go to taskmanager.
My Event Viewer showed "The driver nv4_disp for the display device \Device\Video0 got stuck in an infinite loop" but the game's played fine since.
Luckily, Psychonauts hasn't given me a problem. I've installed it on my laptop, too, but either the video on it is too weak or I don't have enough RAM (1 GB installed, including video RAM).
<No way you can read this. My handwriting's illegible>