The power supply board of those TVs is known to fail.
It is hard to find and expensive and a logical first suspect in your situation.
We do not have it, but we will likely be able to test it and, since this is what we do, probably have good chance at fixing it.
We do not currently officially offer a repair for it however you are still welcome to send it through
www.coppelltvrepair.com/newservice.
Price, if successful, will be in the range of other 42'' power supply boards we repair and at any rate less than what you'd pay for a replacement if you find one.
If we don't fix it you'll only pay return shipping of about the same as what you'd pay to send it to us.
And if the board turns out to be fine you'll pay about $20 diagnostic fee plus the return S&H.
You can spend some time at
http://blog.coppelltvrepair.com where there is a number of articles on how to test different LCD TV power supply boards; the mechanism will be the same for yours and if you apply the same logic chances are you can actually test it on your own.
Prices and conditions are valid at the date of this posting and can change in future.
Sorry I can't help better, but I just have not worked on that board yet.