Hi, I've got an iMac G5 1.8 running Panther so I was trying to upgrade to Tiger. Got halfway through the upgrade (not sure at what point) and restarted. Then it continued spinning, and spinning, and spinning (Apple icon appears and the spinning is below). Force shut off, unplugged, got install disc out and restarted and same thing is happening. If I hold down "c" this computer won't start from c.d.... also I hold down option key and fan goes beserk and freezes up. The overheating component was replaced a few months ago. (it's a revision A) ANY SUGGESTIONS?????????