There were hundreds of models with the Bravia label so nothing specific can be offered. For the old tube models I'd say it's a board failure. For the newer flat screens it could be a board, connection, or panel failure.
It has never been a setting or user serviceable item.
We have swiched on TV this morning and it has two ribbons/bands down either side of the screen which are advertising various things - Bravia etc Not sure how this has happened - how do we get rid?