Hey, I have a Power Mac G5 with two cpus and I swapped out one of the processors, because I thought it was defect. When I started my mac just with the known-good old cpu which I didn't swapped it worked well. But when I started it with just the new cpu I had swapped it worked too, but the fans are very loud. I then put both cpus in (the old good one and the new one) and the fans were still really loud. I did an Hardware Test and there was just a weird RAM problem. Then I installed Mac OS 10.4.3 but still the same.