It sounds like the connection from the LCD screen to the main board isn't quite right. Unplug the device from power. Watch [https://www.youtube.com/watch?v=3vzlNihjqR4|this video] until about 2:10, which should help you remove the back cover from the television. Then, check the main board-screen connection and make sure it is secure. Also, check for any bent pins on the connector itself.