Another iBook not booting

I have an iBook G4 (about 20 months old). I was using it to browse the internet for a couple of hours yesterday evening, quit my internet connection, unplugged the USB modem and closed my iBook (without shutting it down). About an hour later, I opened it again, but the screen was completely black. It wasn't turned off, though, cause pressing the power button didn't show any effect. So I pressed the button for a couple of seconds and I could hear that it turned off. I turned the iBook on again, it showed me the grey screen, the apple logo and the progress circle thing. But then the progress circle stopped... well, progressing.

I tried turning it off and on a couple of times, but it didn't work. So I tried every advice from the handbook, but that didn't help (mostly cause I can't insert the install/restore CD). I tried the double-boot thing, that didn't help. Pressing the shift button doesn't show any effect at all. Resetting the PMU doesn't help. I can boot in single-user mode, but can't do much with it, because the iBook just stops working again after a few seconds and I can't type anymore... it just freezes.

I really need it to work, cause finals are coming up and a lot of the stuff I need to know is on there.

iBook G4 Mac OS X (10.3.9)