why does my ibook only have a white screen when I start up

Well it would be help to know which model you have, G3 or G4 ?

But it sounds like motherboard or display panel/cable defect. Do you get the start up chime, is the hard disk accessed and if it is, if you wait enough and then try to adjust volume via volume keys, can you hear anything. If not, then it is maybe the motherboard, there was this component which failed very often in iBook G4 laptops and I think there was also graphic chip failures, later models suffered from the Airport connector becoming loose.

But, tell the exact model, it helps.

So it is iBook G3:

http://www.everymac.com/ultimate-mac-lookup/?search_keywords=M6497

Because it does not chime and displays white screen I think it is motherboard problem. You should however try to reset PRAM ja PMU:

http://support.apple.com/kb/HT1379

http://support.apple.com/kb/HT1431#faq5

But I don't think those will help in this situation, but try. You could try removing additional memory stick (if installed) to rule it out.

If Mac OS X 10.2 or later installed, you could try starting up in Safe Mode:

http://support.apple.com/kb/HT1455

Also, this Apple Knowledge Base article may be of some help:

http://support.apple.com/kb/TS1417