Zapping the PRAM. Hold down the Option key + Apple key + R + P immediately after the first chime and wait for the 4th chime then release.
Other than that, you are currently doing all that can be done. One other suggestion. If the above does not work. Unplug the AC adapter AND remove the battery. Leave it alone for 30 Mins and then replace the battery and the AC adapter. This resets the logic board. Try to boot.
Other than that, without the System disks you are in trouble. What makes you think it is a conflict with NAVM7? Is this something that you just installed?
This is the ClamShell iMac? The one with the handle at the back or is it a white one?
P
OS 9.2.2 freezes during startup. I have tried the shift key to turn off extensions. Clock comes up and computer freezes. I have used the spacebar, computer freezes at the extension manager console. I do not have the orig system install disk 9.0.4. Please help. ibook G3 Model #M6411.

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