I can hear it but I can’t see the picture

@millie1960 could be a backlight issue. LG is somewhat plagued with backlight problems. Once the screen goes dark but you have sound, darken the room and shine a flashlight at an angle against the TV screen. See if you can make out shapes, silhouettes etc. If so it is you backlight (most commonly the backlight strips). If you cannot it is possible that this is a main board, power board or even T-con board issue. We would need to know the exact model for your TV as well as seeing the boards. So once you remove the back cover from your TV post some really good pictures of the boards with your QUESTION Adding images to an existing question

Of course you always want to make sure that this is not a cable or sat box issue. Disconnect all the inputs from your TV, then unplug the TV. Hold the power button for a minute or two and then connect one video input source. Preferably a local source like a DVD/BR/ Game Console etc. and see if that made a difference. Also, remove any Roku or Firestick drive you may have plugged in. Those can give you same error as well.