You should have a mini-VGA port on the side of your ibook.
You’ll need to get a mini-VGA (male) to VGA (male) cable, plug the mini-VGA end of the cable into that port [it’ll have a picture of a monitor by it), and the other end into pretty much any PC monitor. If you get a picture on the external monitor then the issue is either with your built in screen (which will need to be replaced), or the graphics driver is corrupted (which you should easily be able to re-download and re-install using the external monitor). If you don’t get a picture on the external monitor either, chances are it’s the on-Board graphics chip [meaning you’ll likely need to replace the motherboard].