This is a very common problem with your tv, what has happened is the power supply has failed, more specifically there are a few caps in the power supply that have most likely failed. The unit will require component replacement to get it working again. A repairman will be required for this repair, you can expect the bill to be around $300.
There is a very slight chance that the problem in on the main board, but I have repaired 100's of power supplies and only had one of them have a bad main board, so I do believe you have the power supply problem as I have mentioned. However if you do have a bad main board, then you could expect the bill to be around $500.
I am sorry that I don't have a magic button or a quick fix for you on this one, but component replacement will be required.
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