LCD screen displaying white boxes; Arduino MEGA 2560

Hi, I am new to Arduino and this forum. I am trying to build a machine to extrude 3d printing filament and using an LCD screen to display commands to prompt user input using a rotary encoder.

The problem I am facing is that every time I supply power to my Arduino the lcd only displays white boxes. I have attached the code and would greatly appreciate any help or information as to why this is happening as I am a complete Arduino novice. I am using an arduino mega 2560.

Thanks in advance.

Main_Code_experimental.ino (53.1 KB)

screen_update.ino (24 KB)

Have you tried to get the LCD to work, by itself, using the examples from the library that you use?

Code will not compile. Where is the screenUpdate() function defined?

Sorry here is the screenUpdate() function

Have you tried to get the LCD to work, by itself, using the examples from the library that you use?

Can you answer that question?