Try power cycle the PLC with the LCD plugged in. If it still doesn't work then you may have a damaged LCD or a bad LCD interface. Please contact the dealer or if you have purchased from us, contact sales@tri-plc.com to discuss about the cause of the problem.
Remember, the LCD is NOT hot-pluggable. So never plug/unplug the LCD into the PLC with the power on as that can damage the LCD display or the LCD driver interface on the PLC.