it come black but have sound

jawoona3 once it turns black shine a flashlight at an angle against the screen. Let us know if you can still see the outlines etc. of the channel. This could be a backlight issue which would require you to take a look at your Power board etc. and check the voltage outputs with a multimeter. Let us know what the exact make and model of your TV is as well.

The other thing to try would be to unplug the set and all video input sources. Then hold the power button down for about 30-0 sec. Plug the TV back in and only connect one video source (Leave the cable box disconnected if you have one of those. Use a DVD etc. and see if that works. Sometimes a faulty cable box can cause a black picture as well)