Unfortunately I don't think you are going to be happy here...
The problem you are describing is very consistent with the complaint we get on allot of these flat panels. The symptom you are describing about 90% of the time ends up being a bad LCD panel and because of the price of repair the set becomes non-repairable. The LCD panel part always cost more than a new tv, which is not good for the consumer (you).
Like I said this is the case about 90% of the time, but without troubleshooting the set we cannot know for sure, there will be no quick or easy fix on this one, only board replacement or a bad panel. If you have some electronic repair experience, and have test equipment we can troubleshoot this problem together. If you do not a new tv or repairman will be required.
I am sorry to give you this answer, I know you were looking for a quick fix or magic answer, but I just don't have one on this problem, sorry.
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