This started very suddenly today. I was in finder looking through some pictures when my screen suddenly turned blue. After a second, it faded back to normally, so I continued what I was doing. After about 5 minutes, it happened again, but faded back. It's be less than a half-hour, I haven't touched the computer but the screen is turning blue than fading back every half a minute or so. Every now and then, the screen stays blue for about 20 seconds. All this while idling. I have no idea what's wrong, this has NEVER happened before. Help.