I see,
There is no option or control combination on the printer that will turn the LCD white or blank. Also What ever option or settings you do on the printer, the DELL logo on start up of the printer should always be there because that is a Firmware indication that it is working.
This only means that the LCD is not working on the printer control panel. Possible Loose connection of the LCD cable to the Printer's board or Worst Bad LCD.
This I would suggest that if your not tech skilled in opening the printer up, you may need to bring it to a local repair tech and Have the LCD check.
Meanwhile you can use the computer's Software control for the printer since it is still printing and I really beliieve it is just the LCD.
Please let me know if you got this info.