To whom it may concern, I was working with a Powermac G4 system which boots dually to OS 9 classic and OS X. I was working with some software in 9 and needed to increase the screen resolution. I turned it up and the screen went black.. as I presume the resolution is unsupported. I rebooted into OS 10 which allows all different screen resolutions with no problem, but I can only get into OS 9 with extensions off [SHIFT] henceforth I cannot load the monitor control panels to change the resolution to one that the hardware permits. This is perhaps an easy issue to resolve but I have of yet not been able to as I am no Mac afficionado. Also, the monitor is not an Apple display. If anybody has a clue, please help me out.. and if any other information is required let me know. Thank you..
-j

Try booting with the extensions disabled then locate and
trash the display preferences file in the Preferences folder. It
should revert to the default 640x480 when you reboot.

Thank you, I will give this a try. However, will I be able to change the display back to what it was initially set to [800 x 600, I believe] if I trash the display file?

If you where running it before, you should be able to run it
again.