My tv has sound but no picture

Its probably because the backlit leds fused out. I had the same issue with my LG 32in and i needed to replace whole panel incl the power supply for 180$
 
Need more info.

What is the video source (cable, satellite, Over-The-Air Broadcast)?
What is the model number of the RCA (there is probably a dozen or so 42" RCA flat screens)?

-Wolf sends