You could try ant. on the tuner of the television and try to see if it grabs any channels on AIR ..if the scan goes all the way without finding any channels then the tuner of the television is not working. This means the mainboard will have to be exchange or repair..
This company called Amergence Technology is a 3rd party repair center and is able to offer repair services.. they could give you an idea on the repair cost and the process they have in place..
there number is 866-965-3842