ibook G4 not booting up

I have an mac ibook G4 which i,ve had for nearly a year, it suddenly decided it does'nt want to load its operating system. After the apple logo it stays on a blue screen then after what seems like forever you may get the message spotlight unexpectedly quit and wants you to relaunch, which has no affect.
does any one have any suggestions.

I'm having a similar problem with my powerbook g4. When I turn my computer on, the login box appears and then disappears, and Im left with the background image screen. The computer is still responsive, but it doesnt proceed any further. The only thing Ive recently changed is the airport configuration to a new access point.