There are quite a few possibilities. Just for one, the battery was barely-charged, and the presence of the CD-ROM drive (which is constantly polled by the system 'in case' there is a CD inserted) depleted the battery, especially on top of its normal power consumption, too far for booting from cold.

The PB should be able to boot from the adapter alone,, which will assure you that the PB is functional. If it does not, you may have to reset the PMU. A few minutes on the adapter will achieve precious little recharge, so allow at least 24hr for an unknown battery before expecting significant improvement. Do you have a VOM for testing the battery's terminal voltages? They do not equate with full charge, but are indicative of battery-condition.

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