If you had to unplug the power cable as part of the detangle process, I suspect you have a dead internal battery, or "PRAM" battery. That battery maintains settings while the computer is off wall power but, given a life of 3-5 yeras, one that's dead when the computer is unplugged can makethe computer forget a lot of stuff, like where its startup disk is located.
The battery in the iMac G4 is not considered a user-serviceable part as it requires a level of disassembly not normally undertaken by amateurs. If you feel you have the expereince or inclination, google "G4 iMac takeapart" for instructions on how to get to the innards. Understand that failure to follow the reassembly instructions accurately can result in overheating that kills the computer.
You can often get around the need to replace the PRAM battery in a situation like yours:
- Start with the OPTION key pressed (if you are using an Apple keyboard). Keep holding until you see icons onscreen indicating startup discs. You may have to wait several minutes before being able to select a disk. However, once you do, the computer should start properly as long as you leave it on wall power.
- Start from a system install/restore CD or DVD, or from any Mac-bootable optical disk. Once the computer is running, use System Preferences > Startup Disk to select your internal hard drive.
- Cold-start the computer while holding command + option+ p + r and keep holding that key combo until you hear three startup chimes. That resets the PRAM and hopefully will point the computer to it proper startup volume.
