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Just to get all technical here after the fact -- a CRT TV has 3 electron guns in the tube, Red, Green and Blue. It looks very much like your Red gun and/or Red and Blue guns died, leaving the whole thing green.

This used to happen a lot with CRT computer monitors, and you could almost always fix it by replacing the cable because it was usually a busted wire in the RGB cable.

Danger, Katie Robinson! Just before you go fishing in the back of the TV looking for cables, there's enough voltage in a colour TV - *even when it is off and unlugged* to kill you. Do not open it up unless you know what you are doing and have non-conductive TV repair tools.

The slam upside the case works in the instances where it;s just a loose connection, but your problem may also be component breakdown.
 
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