Ok, thanks. This is a pretty typical LCD scenario, believe it or not... quite common. ESPECIALLY with these Samsung models.
These sets can get what I like to call "borderline bad" components... hit and miss when it comes time to power up. Eventually, and as you've seen, the components will get worse. With time, they'll fail completely (you might be at this stage already). The components: capacitors in the power supply circuit.
If you or someone you know is handy with a multimeter and soldering tools, and you want to repair this... I recommend you start there. The power supply will be the first circuit board you run into if you trace the input power cord. Look and smell for burnt or open components, paying particularly close attention to the capacitors. If any of them are bulging/swollen (not perfectly cylindrical), domed (not totally flat on top), or leaking... they are faulty and will need to be replaced.
Else, consider replacing the whole board. It will be slightly more expensive as far as parts are concerned... but will save you on labor. The board will run $50-$150 depending on which version you have.
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Kindest regards,Dan T.