Ok. I got a Powerbook that did not power up when plugged only to the A/C adapter, BUT...the Powerbook powers up with a charged battery. Now...initially, i had thought there was a problem with the DC In-board. I bought a new one, installed it, and the problem still exists. It sounds like the A/C adapter gets grounded when it plugs into the power plug on the Tibook. Does anyone have any other suggestions for me to try before I think it's the logic board itself?