Scruff,
A powerbook that is stored for long periods usually develops a severely corrupted power manager and this often cannot be cleared in the normal way. However, give it a try (with some modification):
1. Remove the main battery and disconnect the power adapter. Note: Please make sure you have power at your A/C outlet.
2. Press/hold the reset button on the back panel for 30 seconds.
http://docs.info.apple.com/article.html?artnum=58416
3. Connect just the power adapter and try starting.
4. If no success, repeat steps 1-3 several times.
5. If still no success, remove all power for 24 hours, then connect just the power adapter and try starting.
6. Failure at this point requires disconnecting the internal rechargeable backup battery (PRAM battery). This is often the only solution to a severely corrupted power manager. Another factor also comes into play: If the PRAM battery has developed an internal short, you will never start without disconnecting the battery, and by the way, a powerbook runs just fine without a PRAM battery, unlike a desktop machine.
If you want to take the step of disconnecting the battery, please post back.