So, I have an iMac (24" model with the 3.06GHZ processor) and the hard drive went bad. When I booted with an OSX disk and ran the disk utility, the drive didn't even show up. I pulled out the drive and hooked it up to my Macbook pro with a SATA to USB converter and it wouldn't even power on. It's out of warranty, so I just purchased a replacement drive (500GB SATA). I've replaced 4 before in different iMacs and this time went like any other. Once I buttoned it back up, I booted from a Mac OSX 10.5 disk and it told me I couldn't install to the disk. I figured it was because I was using a newer OSX disk from another iMac that I had lying around. So I left it on while I dug around for the other disk. I finally found it after roughly an hour or so (didn't look the whole time), rebooted the Mac, and then I got an error. It was a gray screen telling me to reboot the machine. It was then I noticed the iMac was hot, almost too hot to touch comfortably up near the big intake vent on the back. I guessed that was the problem. I left it off for a while, pulled the aluminum case off and tried to boot with a 10.5 disk I had. Same gray screen telling me to reboot even though it's cool. I then thought maybe my disk was bad and I grabbed a 10.4 disk I had. Now, it bongs, you hear the disk being read, then it reboots. What am I doing wrong? I've done this a few times and never had this problem. The only thing that is different - The new drive is super skinny. The old drive is an inch high, the new one is less than half that. So it doesn't fit quite as snug as the old one. I'm a systems administrator for a large college in Arizona. Just so you get an idea of my skill level - I have access to a lot of stuff to determine the problem if anyone needs more information. This one has me over a barrel.