I hope this is the right forum. On my G4, the screen is a very very dark gray, and I can barely see anything on the screen. It just randomly went to that gray screen (its like a light is out or something). I have tried messing with the controls and conifiguration but nothing is working. If this is too vague let me know, but if not and you have some suggestions, please share them. Thanks in advance.
There is a chance that a backlight bulb has gone out in the LCD panel. Have you tried adjusting the brightness up and down to see if it changes at all? If there is no change at all, then that might be the problem. I don't know the part to reccommend, but you'll have to take apart the display housing, get to the LCD, take out the CCFL tubes and replace them. Of course it could be the backlight inverter too, but I'm not sure if that is in the LCD housing or if it's down in the dome. I'd bet on the LCD housing, though. Get a service manual and check all the cable connections be fore you get too far into deciding to order parts, etc. Also giv ethe plugs a good looking at for scorch marks, etc.
Did you just upgrade to 10.4.8?