My boss has a G4 iMac with 10.4. He did the most recent security update and when it rebooted it made the gong sound and then sat for about a minute with a black screen. After that minute the fans kicked in on overdrive and nothing happens after that. I unplugged everything from the machine except for the power plug and rebooted. The results were the same. I also tried booting up using the 10.4 disk that came with the machine and held down the C key. Still nothing worked. Any ideas or suggestions?