Apple Studio Display 17" (M7649) won't turn on.

I'm trying to set up a PowerMac G4 450 (AGP), so I just bought a used 17" Apple Studio Display (M7649) and an Apple DVI to ADC Adapter. The previous owners of both items said they tested them and they should work.

The behavior I can observe is a little odd. When I tap the power button on the monitor, it flashes amber then fades away. The screen stays blank. On the other hand, some signal is still getting through the DVI to ADC Adapter, because when I turn on the computer I can change the volume with the keyboard (which is plugged into the monitor).

Any idea what's wrong?