This is probably not the answer, but does the light on the AC adapter plug stay steadily on and not flicker? I've seen some that are so touchy that the computer will power off at the slightest touch. This can either be due to a flaky AC adapter, or a flaky DC-in. A lot of PowerBook power issues can be fixed by the replacement of the DC-in board, but on a PowerBook it's a fairly extensive procedure, and it might not be the answer, so if you have the recourse of returning the item to the eBay seller, that might be the best option.