I had something maybe the same happen when I connected the Xbox via component input (1080i) and then tried to change to HDMI. The Xbox went black (couldn't be seen) so it was impossible to get right. I finally plugged both HDMI and composite in the TV; selected
the composite input, set the Xbox to 1080p (at which point the screen goes black); selected the HDMI input and voila! All was good! Then I disconnected the composite input and haven't had the trouble since.
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