I have a MacBook that's about 3 years old. Recently, the screen has begun to behave erratically. At random times, the image will slowly become grainy, and then fade to white. Starting from the center and working outwards, the white image then becomes a negative. Finally, the negative image slowly fades to black. During this process, I can't move the cursor or interact with any applications. After a minute or so, the black screen will suddenly resolve itself and return to normal. This has happened to me a number of times while running OSX, but also while running Windows XP through bootcamp.