If you tried everything that has been advised in this thread, and if no third-party components have been installed, and it still doesn't work, I'm afraid Testuser is right : you have serious hardware issues.
If this happened just after a new install, it's possible your HD has been corrupted, and so your firmware if CD booting isn't enabled.
If your iBook is brand new, giving back to your Apple Dealer is a good solution for sure.
Anyone has any idea before ?