Numbers are not showing up on the display

Most likely the either the LCD display itself, or the printed circuit board has developed a crack, and some of the signals that drive the display have been interrupted.

To inspect the printed circuit board, follow this guide (basically taking the rear cover off is all it takes).

The LCD is not repairable. The printed circuit board may be repaired by someone who is reasonably skilled with a solder iron, the operation entails bridging the interrupted circuit tracks with pieces of thin copper wire.