Geeetech

Either the LCD cable is bad, the LCD cable is not making a proper connection or the printer might not be getting past the bootloader and loading marlin. Unplug the printer from any USB connection and turn it on. Try and move the stepper motors (X-axis for example). If the motors are stiff and holding their position, Marlin isn't loading.

If they are moving something's probably wrong with the LCD cable / connectors.

Edit: Black bars means the LCD is not initialising. Contrast shouldn't need to be set on the LCD at all, but could (in theory) be modified with soldering if you really wanted to.

Hi, you can 1. Try to reconnect the LCD wiring; 2. Measure whether there is 5V voltage on the motherboard; 3. Manually install the driver
I hope this can help you.