Display backlight is on, can hear OS sounds, but no picture - iMac G4

We turned on our beautiful iMac G4, everything seemed normal until I noticed that I never saw a picture on screen. The backlighting works (I can even increase and decrease the brightness of the "black" screen) but there is no picture. Computer works as I can still hear the OS feedback sounds. I would love to keep this model but wonder if it is something common (and easily fixed) or uncommon (and too expensive to fix to make it worth it).

Thank you all in advance!