Chosen Solution
It will power up from a battery (charged from another iBook) but will not power up, or charge the battery, by the power cord. Is this an issue with the DC-In Board?
What color is the AC adapter plug when it’s connected to the computer, and does it seem to change when you twist it around? If so that’s evidence pointing toward the DC-in. If it changes color, or at times has no color, try adjusting it until it’s green, and then power on. Again, if it behaves this way, it’s the DC-in.
It’s either the charger or the DC-IN port. Try the charger on the other Book. Check the end of the plug in on the AC charger to see if it is broken off.
