Screen is fully blacked but camera still shooting

Was this camera ever dropped or jostled hard to create damage long after the event? Digital cameras have several separate functions as you see with the display electronically driven while some of the camera still retains mechanical functions. A quick remedy might be removing battery and memory card for a minute then replace only the battery (forcing a reset to factory defaults). The screen may turn on with all characters turned on as part of self tests or just display normal info. Observe this power up for clues. If the screen remains dark then you may have to turn to Canon or professional repair service. If the screen turns on then lack of memory card may be detected with an error message to prompt you to power off and put the memory card in and see if display functions return to normal.