Your next step would be to do an ALTBoot. Sadly we are not allowed to post how that is done on the forum. That would wipe all data and reload the firmware straight from a USB drive.
If the screen stays messed up after that you would know for certain it is a hardware failure and would have to diagnose from there. You would need a Service manual for that, and again, we can't post links to those either as they are considered internal information.
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for posts that resolve your issues. Your feedback counts!Joe Arseneau