Chosen Solution
Lets review the boot process: About the screens you see when your Mac starts up. A Bad HD would get you blinking question mark on a folder icon. So it’s not a bad drive. You can also prove this as holding down the keyboard T should show a FireWire Icon floating across the screen as you are telling the system to go into Target Disk Mode: Use target disk mode to share files between two Mac computers If you have a second Mac that can connect to your iMac you should have access to your systems drive. But I don’t think you’ll get that far. The fact the external monitor shows the same screen aims us to a logic board failure.
