Help with an iBook G4 that won't charge

I am the owner of an iBook G4 14" that was purchased last August. I recently noticed that when I charged my iBook, the light no longer came on. Also, I could maintain my battery level, but the battery meter would not charge. I initally thought the problem was with my power adapter, but tests with different power adapters and different outlets ruled that out. Then, I thought it was the lithium battery, but I was able to charge my battery by putting it in another iBook. So, the problem must be with my computer. Does anyone know how I can get this fixed without having to pay for the AppleCare Protection Plan? Thanks