I fixed a few of these... Your issue is more than likely to be with the graphics chip. Easy way to tell if this is your issue to open up your Xbox360 and apply downward pressure to the graphics chip when turning on your 360. This doesnt always work!! The only two ways to fix it are a: X-Clamp (google it) or b: get the graphics chip re-flowed.
I fixed a few of these... Your issue is more than likely to be with the graphics chip. Easy way to tell if this is your issue to open up your Xbox360 and apply downward pressure to the graphics chip when turning on your 360. This doesnt always work!! The only two ways to fix it are a: X-Clamp (google it) or b: get the graphics chip re-flowed.
All the best
Justin
ConsoleFixers.com