It is most probable that there is a failure on the power supply board inside the TV. Commonly the capacitors on this board will receive a surge and then fail. They can sometimes be visually verified by removing the rear of the set and inspecting them for bulges or leaking fluid at the top or the base of the caps. This is the most common mode of failure for these sets.
The capacitors are located on the power board inside the set, where the AC cord plugs into and can be replaced by a Tech for no more than $150 parts and labor if this is the case. The power board itself will run you roughly between $35-$100 to buy the part.
The set definitely requires component testing and replacement in order to get it to function properly again. Unfortunately there is no sequence of buttons or reset you can perform to get the set working again.