This aticle explains and provides a workaround for a situation in which no video is available on a Apple Studio Display 15" LCD when set at 1024x768 at 72Hz.

I have an Apple Studio Display 15" LCD connected to a Power Macintosh 8500. When I select the resolution 1024 x 768 @ 72Hz my display loses video and the message "Signal out of Range" is displayed. I have tried restarting the computer and selected the reset button on the front of the display but the situation remains. How can I restore the video?

Solution :

Although the 1024 x 768 @ 72Hz resolution setting is available before you install the Apple Display Software 1.6 on a Power Macintosh 7500, 8500, 7600 and 8600 CPU, this setting does not work with the Apple Studio Display. If selected, the display will lose video and the following steps must be performed in order to restore video:

1. Press the power on key on the keyboard (arrow pointing left on the upper right hand corner of the keyboard). You should hear an alert sound.
2. Press the R key to restart the computer.
3. At the startup tone, hold down the Command, Option, P, and R keys on the keyboard to reset PRAM. Continue to hold down these keys until video is restored.