Hello there and welcome to Just Answer. My name is XXXXX XXXXX I will be assisting you today. I am an engineer with over 30 years of electrical and electronic training, repair and installation experience. I will try and answer your question accurately and precisely so that we can get you on your way.
Now...This could be several things things , the TV definitely has an internal failure. I will try to explain the possibilities the best I can. The biggest issue facing you here is that repairing a set this size is almost never economical.
Your power supply board is very likely faulty. This is common on these newer flat panel
sets. This fault is usually caused by bad capacitors (leaking or bulging) on the board but could be also some other components or combination of issues with that board.
Less likely is the Main board, the TCON board or the actual LCD panel.
If the TV is under warranty, let me know.
If it isn't and if you are handy with a screwdriver, we can do a visual confirmation and a couple of tests by unplugging various boards and seeing if the voltages are present at the power supply.
Can you do this do you think? If so, remove the back and we'll take a look. You would need a multimeter capable of measuring DC volts and resistance.
If not, give me your zip and I'll find you a tech in your area.
The cost for the board is usually under $100. I can find you one. To have this repaired is going to cost you $250 and up - clearly not economical since a new one costs about the same.
I am sorry that I don't have a quick fix or easy answer for you on this one, it is definitely an internal failure. Let me know how you want to proceed so that we can continue.