At the tech dept we have this G4 that refuses to boot past the grey screen with the rotating wheel. The logic board has been replaced, we've removed all sticks of RAM save 1x512, we've tried a known working optical drive, replaced ribbon cables (optical cable was frayed on one end) No dice. Option booting works, but once we select the DVD we can't boot from an install PPC CD either, it just gets stuck at the grey screen. We also have a tech HD inside that the computer does not boot from either. any suggestions?