Boots from battery, not from power cord
I rescued the machine in question from being tossed in a dumpster. It will power up if I charge its battery in my own 17" PowerBook first. But it will not start up without the battery when I plug the power cord in, nor will it charge the battery. The power adapter I tried is the original that came with my (identical model) 17" PowerBook. I'm thinking the DC-in board needs replacing.
Is this a good question?