Black screen, no logo and already replaced LED backlights

My LG TV (model 47lb580v) had faulty back lights which were replaced and are now fully functional. However, when I turn the TV on the backlight kicks on but I don't have any picture at all. I have triple checked all of my connections and replaced the main board, audio board and the t-con board but I have no picture at all. Not even the LG logo comes on when I turn the TV on.