Sound but no picture

@ibrahimhanafi just to elaborate on the excellent answer by @honakrisi turn the TV to a channel where you can hear the sound. Next, use a flashlight and shine the beam at an angle against the screen. Do that in a darkened room. See if you can make out shadows or shapes. If you do, then it is your backlight that has failed. If you do not see anything, unplug your set and remove the back cover. Then visually check the boards for any obvious damaged components. Check all the wiring and unplug the wires and plug them back in, make sure they are properly seated. Post some images of all of your boards with your question. Use this guide iFixitでの質問に画像を追加する方法 for that so we can see what you see. It is possible that this is either a power board or a T-con board issue