How long have you had the set for and when did the problem occur?
Does the power light on the front fo the set blink?
Please try this, shine a flashlight directly up against the screen of the TV and look very very closely at the screen. Do you see a dimly lit image behind the screen?
The problem is that the backlight inverter boards (Slave and master), or the power supply output rail that feeds the inverters has failed. The power supply output needs to be tested for voltages both under load and no load to determine which board has the fault. Unfortunately there are no resets or buttons you can press to fix the problem and the set will require service. Average cost for this type of repair is around $250 parts and labor if the inverters are found faulty, or also $250 parts and labor if it's determined the power supply is the culprit. The problem is going to be either one or the other.
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