I have sound but my picture keeps going black

Karol Varga since you can see your screen with a flashlight you already know that this is a backlight issue. It can be that your power board does not generate the voltages needed for your lights to turn on or that the backlight array inside the panel have failed. You can either measure the voltages and try to find out why the power board is not working, or you can replace it. Get it from somewhere that does have an easy return policy. If a new PSU does not resolve it you know that it is the backlight array. You can fix that be disassembling your panel and replacing the strips. Not a terribly difficult job just a bit of a PITA due to the size of the panel.