likely the pins in your LCD connector are likely built up with dirt. Open the device, remove the LCD connector. use a toothbrush and 99%isopropyl to scrub at bot the gold traces at the end of the flex, and inside the female connector of the board. Air dry for 10 minutes, and reconnect.
This SHOULD Fix your issue.
If it does not, either the flex is damaged, or the connector on the mother board is damaged.
-if the flex is damaged, replace the LCD
-if the connector is damaged, remove the connector, and solder a new one onto the board. (This last step is a more difficult procedure, and without SMT Soldering experience, i would suggest taking it to a professional.)