picture won't come on, but the sound does. model#T420HVN050. 5yrs old

jdg_johnd could have multiple reasons and you will have to do some trouble shooting. Remove the back cover off your set and take a look at all the boards. Check to make sure that all cables are properly inserted. Check your boards for any obvious damage like domed or leaking capacitors. Then you need a multimeter and check the fuses on the power board as well as the one of the T-con board, for continuity. you need to unplug your set for that of course. Post some good images off all of your boards with your question. That way we can see what you see. For that use this guide 在已经存在的问题里加入图片 Right now it sounds like you either do not have a backlight due to a bad power boards or LED array. Or you may have a bad T-con board which can cause the same symptoms. Let us know what you find.