Ok, thanks. There are a couple possibilities here. I'll do my best to give some insight into each.
First, it could be your power board. This board takes the line input... chops/rectifies/filters it, and sends out a series of insulated DC voltages (3VDC, 5VDC, etc.). A fault here could very easily explain your symptoms because it's the base for everything else. Repair here will vary depending on where you live, and on part availability, but usually runs $250-$450.
Next, it could be the main board. This is your TV's main processor, so to speak. It controls the logic functions, and most I/O capabilities. So again, this could be your issue. Repair here will be more than the power PWB, usually by $100-$200.
Finally, it could be the LCD panel itself (the screen), though this would be much more rare. This would be far too expensive to replace.
I wish I had a more definite answer on this one... but there really are a couple possibilities.
You'll need to hire a technician at this point. You'd be looking at $50-$75 for a diagnosis, but that'd be put toward the final bill should you decide to have it repaired.
If you want, you can post back here with the tech's diagnosis. I'd be happy to let you know what I think.
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