I just tried replacing the hard drive in my aunt's old iMac G4. Before the Mac Os X installation disc couldn't find a hard drive to install on. So I just replaced the Hard Drive today with a 80 GB seagate hard drive. Now, the same thing happens and Mac OS X can't install. I went back and checked as much as I could. I didn't want to actually take out the hard drive again and see if it is connected until I got some answers on here. I hear the Hard drive running, at least I'm pretty sure I'm hearing it and not the disc drive. But it still won't show up. Is it simply just a hardware problem, or what? Or else is it because I think I am using just a mac os x upgrade disc because I believe the machine originally had Mac OS 9 on it. Do I have to get my hands on a copy of the iMac's mac os 9 restore discs? Any help would be great.