Black Screen, new inverter, different logic board?

My daughter inherited our old G4 several years ago. Recently the screen went black and the startup chime ceased to work on the internal speaker. You can see the desktop with a flashlight and I can access all functions normally that way.

I replaced the inverter with a new one, no change. I replaced the logic board with a used one off ebay said to be good. Startup chime started working, red LED power light comes on, disc spins and makes the spin-up sound at the point where the screen would normally light up. But the startup terminates at this point as if the power cord has been suddenly unplugged.

Reinstalled the original logic board and it will boot, but no screen, no chime. PRAm/PMU/SMU all reset. No external monitor or Apple super-special hi-dolla cord to plug one in.

Is there another way to test the monitor? Can it be plugged into my current desktop, a 24" Intel Core Duo 2.8mhz? Thank you for any help.

Richard