Lg problem 50pv400

First of all Hello to everyone, Im new here. Im trying to help a friend that has a lg 50pv400 model. Is tv turns on for about 5 seconds then turns off.
I plug 2 light bulb in serie from the vs and the gnd . It turns on for about 5 seconds and then shuts down. When I unplug the main board , the power stays open. Anyone got any idea what I can check next. Thanks.