I'm going out of my mind trying to fix g4 imac and I've been working on computers for 25 years. It wont boot up right in any way. I have put a new hard drive and motherboard battery in it, cleaned it and checked everything. i have reset PMU. The computer will start and make chime then black screen. Sometimes screen comes on. The imac has no system on it, and it will not look for CD if system cd is in it, but most of the time I cannot get cd drive to open on boot up, basically it is freaking out every way there is. Any ideas? The computer is pretty much chiming, then blank screen, will not open cd tray on startup. Ram has been re seated its been cleaned, and connections checked. So I have a screen that comes on rarely, a cd drive that opens on startup rarely, imac will not boot from correct system cd if I get one it in it. Multiple unrelated problems. Last time I saw this on a mac was twenty years ago working in IT and I finally found a small paper clip lodged under motherboard of a Power Mac. I'm lost at this point, I don't know what to try next.