The simplest method is to check the LED status indicator on the Vizio TV.  If the LED lights are blue: the TV is supposed to be on and working. However, if the light is powered down, the TV is not receiving any power.  Therefore, if you have confirmed that the wall socket and the power cord have no defects and the light on the status indicator is still powered down, this may indicate a faulty power board/power supply unit on the Vizio TV.