Hi! I'm wondering if this happens in all screen resolutions and color depths? You might try switching to a different resolution just to see. While unlikely the answer (due to the fact you've tried two different operating systems), I have seen machines go into odd screen resolutions when a DVD is played, or when external video is used (I assume to accommodate the limitations or specs of the external image). Also, I always do PMU and PRAM resets on malfunctioning machines, just to rule that out, because funky settings in PRAM can cause any number of problems. Hope that helps.