I recently had a problem with my G4, it took 4 hours with tech support to determine it was a hardware problem. So into a shop the computer went. The outcome? The motherboard is fine but it turns out its a power problem. I had the computer connected to a power strip with a surge suppressor but (I'm guessing) because of everything else attached to the strip it caused fluxuations to the power. Once I plugged the computer directly into a surge suppressor and directly into the power socket - problem - gone. Dan