My iBook g4 can't run Mac OS X (10.4.9).

After the "Boing", I don't get anything on the screen, until it shows "Starting Mac OS X" with the loading bar. Then, the screen shows the finder, the dock and becomes black. I get the sleeping LED, but there's no way to wake it up.
I get the openfirmware command prompt without problem, but is there a way to disable sleep in the openfirmware?

I tried:

1. To plug a USB keyboard and a mouse on the ibook and to wake it up
2. To reset the PMU and the PRAM
3. To bypass the sensor in the lid
4. To call Apple Support
5. To pray Steve Jobs

But nothing solved my problem. Is there anyone who can help?

PS: Sorry for the English level, I'm French.