IBook g4 won't start up!

Hello,
My ibook g4 won't start up I turned it on and the chime goes as normal but the screen appears with the apple logoas normal and the swirly loading sign but stays like that for hours and doesn't go to the log in page I'm new to this lap top and I have no experience like this before please help me!!
If you know how to fix thIs problem kindly email me on ilytaylor1995@hotmail.com
wating for your replies. Thank you :( please also explain clearly because I am only13 and I dont really understand computer languge like cmd?
So its a mac Osx not sure which version and I can't check it out obviously because i cant log on!