Apple Studio Display - No Access to Brightness Control


Hiya, i have a G4 w/17" flat studio display - it has an ADC connector. The problem is i no longer have access to the brightness controls. Th bezel button brightens when i touch it
but does not bring up the display prefrences window. When i
open display pref. in system pref. i have only the the display resolution, calibrate and color options - no brightness or disable bezel button - I have had brightness control up till one month ago, can't seem to find help on this one. I appreciate your input.