Symptom
With any of these computers -- Quadra 610, Centris 610, Quadra 660AV, Centris 660AV, Quadra 800, or Quadra 840AV -- is used with the Apple Basic Color Monitor, 1152x870 and 800x600 at two different hertz values are available in the options portion of the Monitors control panel. If any of these values are selected, the screen will turn black or a distorted image of the screen will appear.
Solution
Resetting PRAM, which resets the system to the default 640x480, is the only known fix.