has sound but no picture, backlight is good

@simom first thing you want to try is to reset your TV. Unplug the TV for a few minutes, then plug it back in. Sometimes this clears any issue. You also want to check all of your TV's inputs (HDMI, COmposite, Coax etc.) and see if the results are the same on all of those. If it does not work you will most likely have to remove the back of your TV and take a look at the boards. Post images of those with your question. That will allow us to see what you see. Use this guide for that. The list of possible failures includes the power supply, the main board, the scan drive or sustain boards, T-Con board and of course the panel itself. Most likely this will be a Main board issue.