Bill Gander : The instructions I posted were specifically meant for the later generation iSight models of the iMac G5. If you have an older iMac without the iSight camera the issue probably lies with bad electrolytic capacitors. Those caps are found both on the logic board and inside the power supply, and sometimes can be faulty even without appearing deformed. The first thing I do with those is always replace all suspect capacitors and that solves every problem present 90% of the time or so.