Resetting PowerBook and iBook Power Management Unit (PMU): "The Power Manager is an integrated circuit (computer chip) that is usually on the logic board of the PowerBook and iBook. As the name implies, it is responsible for power management of the computer. It controls backlighting, hard disk spin down, sleep and wake, some charging aspects, trackpad control, and some input/output as it relates to the computer sleeping.
Over time, the settings in the Power Manager may become unusable, which can result in operational anomalies with the computer. Examples include not turning on, not waking from sleep, not charging the battery, or not seeing the AC Adapter, among others."