My friend is using a Power Mac G5 and it will not shut down. When shut down is selected, it gets to a blue screen with the rotating progress wheel, or whatever, that is seen on start up. It will stick to this screen until the computer is forced off by holding down the power button. Also, occasionally, when the computer is powered on, the fan runs at full speed and nothing happens until it is forced off and turned on again. I'm guessing these two issues might be related. Any suggestions on what to do? We have tried unplugging all USB devices.