I just recently got an iBook G4 from a guy on eBay.

When I boot, I get a black screen instead of the grey screen and the spinning wheel. I then get the blue startup screen correctly. Ive tried to contact the seller but he/she hasnt' responded for a week. I don't know if it's has something to do with SUM because, everything before the blue screen, you can't see. He also seemed to have only a limited account and a hidden admin account apparantly because I only see one account on the login screen that is limited. So how did this guy make it so that you can't see anything before the blue screen in the first place and how do I change so that I can see it?

It sounds like the seller seriously screwed things up. I'd get a boot disk somehow and see if you can reinstall.

I can't. I tried already. you need a password to do it which i don't have or know how to get or reset, unless ive already done that by reseting the PRAM.

Pull out battery , disconnect power-brick.
Wait for a while,
Power on holding the power-button for 7 seconds
-----------
Try this: http://docs.info.apple.com/article.html?artnum=14449#faq6