From Apple Knowledge Base Article 14449:
The Power Manager is an integrated circuit 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 I/O as far as looking at the serial port and modem so it does not sleep when connected.
Over time, the settings in the Power Manager may become unusable, which can result in operational anomalies with the computer. Examples would be not turning on, not waking from sleep, not charging the battery, or not seeing the AC Adapter, among others.
A reset button is not intended for resolution of a stall or situation in which the computer is non-responsive. A reset should not be necessary except as a last resort in cases where a hardware failure of the power management system is suspected. Pressing the reset button resets the iBook and PowerBook hardware, including NVRAM, and forces the computer to shut down.
For most situations, a restart is sufficient. If the computer has stopped responding, try these steps, in order, until the computer responds:
1. Force Quit (Option-Command-Escape)
2. Restart (Control-Command-Power)
3. Force Shut Down (press the power button for ten seconds)
Only reset the computer if none of the above steps resolved the situation. If this is the case, see below for instructions on locating the reset button or key combination for your model of iBook or PowerBook.
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