The most possible scenario is that there is a dry joint somewhere between the video input female rca connector and the tv board's main signal processor, and a technician's assistance would be a good solution for the problem. Attached here below is a link to your tv model operation manual download. Please go through it and see if it works, if it fails, consider changing the entire main board.
Locate the four holes in the back of your television, you just need to measure the dimensions from left to right and top to bottom. The horizontal and vertical measurement is your VESA.
