Could be dry jointed. This is quite common in Philips and Hitachi TVs and happens when the solder that sticks wires or components to to the board drys up and comes loose. The most common area for dry joints is where the power cable is connected to the board and this will cause it to switch off. Best to take it to a TV repair place and not to try and open it yourself as the tube inside gives off radiation and can be a bit dangerous. It also contains capacitors that store huge amounts of electricity and if you touch one accidentally it can kill instantly.