iBook is dead

What's wrong with my ibook? It's just dead. It was working fine earlier and now, nothing. I usually just close the lid and let it sleep. There's no sleep light. When I open the lid, black. I try the start up button, nothing.
What do I do?

okay... I just reset the pram and that got it working again. WHEW. But it messed up the time and date. Had to reset that. What else would have been messed up? And why did this happen in the first place? What can I do to prevent it in the future? I hardly ever shut it down, should I be doing this?

Control plus Option plus the start button will normally work when it seems dead. Might be best to unplug any devices first and make sure the battery has recharged to 10% before plugging anything back in. (page 63 iBook users guide)

Sometimes it seems to happen when the iBook is shut down with quick keys with too many programs still open, sometimes when the battery is too low and sometimes who the heck knows It's happened to me a couple of times no problems after.