It's gotta be the DC board. It also holds the audio jacks. I had this issue on my Pismo maaaannnyyy years ago, and I had the same symptoms. The DC board was replaced and all worked well.

Also, DC boards seem to be a weakness on the G3 models. The only flaw I have found with the G3 laptops is the DC board.

I also had an issue recently similar to this with the PowerBook G4 17" i refurbished. The power cable stayed orange, sometimes turned green, but it would never turn on. I replaced the part and at this time, I am typing on it. Fixed the entire machine with a $26/shipped part.