Screen suddenly went dark but the backlights are still on. There is s

bigfrostymike this "but there is sound and the back lights are working" can be caused by a bad T-con board or a bad main board. You want to go ahead and disconnect all the video inputs and the power outlet. Then hold the power button down for 30-60 seconds. Connect one video source and the power plug. Then try and see if it restarts. Try all the video input sources as well. If that does not yield any change, it may be time to remove the back from your TV and take a look at the boards for any obviously damaged components. Post some images of your boards with your question. That way we can see what you see. Adding images to an existing question - iFixit Repair Guide

Also, let us know what exact model your TV is.