Is the screen PITCH black or does it glow gently after it turns on? If it's switching on and off real fast, you may have a direct short on the power supply or one of it's loads. If so, it would be wise to use a digital voltmeter and check voltages and resistance to find it.
Quick info on voltmeters and how to measure voltage and resistance --
We will be concentrating our efforts on the TV's power supply board, using that to run our tests. But to be honest, we really can't run those tests until about 3PM UK time on Sunday.
Or 9AM Eastern US time.