The no lights part bothers me. Are the lights(LEDs) on the display working, is everything else working except the picture? Can you try siwtching the TV programs and see if the sound switches too?
If its only the picture, than the video channel is cut on some point. It can be the connector(bend pins, bad contact, not soldered properly and etc.). if its not the connector the second option is the PCB traces, the third option is some component on the PCB traces's path and the 4th option is the LCD needs to be replaced.
Start checking the points that I gave you with a multimeter or osciloscope. When the voltage is cut on some component(meaning no voltage on it) post it here. It can be that the power supply for the video channel is not working.