Well guys, I feel like a complete and utter moron now. It just occurred to me to take a voltmeter reading across the battery cage. It read +0.78V ... not really enough to boot a Newton, hrm? Investigating further, I checked the voltage across two of the NiMH cells. Those same cells I was /certain/ were charged. Just under 0.1V. That struck me as very odd - again, no wonder the MessagePad won't boot! I'm now recharging the AAA cells, hopefully that will fix my problem. I'll report back sheepishly when done.