iBook G4 won't turn on

I have inherited a non-working iBook G4. I would like to fix it and get it working again. The person it used to belong to said she was watching a movie on the iBook, then it suddenly shut off. Now she can't get it to turn back on, even with it plugged in.

The laptop was taken apart (completely) in order to extract the DVD that got stuck in the laptop when it died. I have re-attached the DC-In board and re-attached the power button. That should be all I need in order to get it to turn on. I plug the charger into the DC-In port, the charger lights up, but when I press the power button, nothing happens.

I'm not sure if the DC-In board is the problem, or if it is something else. How can I go about testing the DC-In board to see if it is working or not? Or, what steps should I take to go about determining the cause of this problem? What should I do?