iBook - G3 600mhz ibook very strange boot problem!

Hi All

This is my first post on these boards. I repair logic boards and my hobby is bringing ibooks back from the dead. I have done 15 successful graphics chipset reflows and hope I can provide some help on the boards!

Anyway.

I have the bottom half of a G3 600mhz ibook sitting on my bench (with a vga screen attached and keyboard and mouse) which refuses to boot on its own accord!

Here's what I have tried so far

1. I have stuck a new hardrive in with a fresh install of osx this is my "Test" drive so I know it works. I try to boot from this test drive but it wont boot I just get the flashing folder icon.

2.I have sucessfully booted from a G4 ibook (in target disk mode) which is connected to the G3 via firewire. And I can do everything on it surf the net etc. And what's scary is that I can easily read and write to the "Test" drive!!!

3. I tried to boot an AHT cd for the G3 by using a firewire cd/dvd drive. I start up in disk manager and I can see the CD I try and boot and the screen flashes and kinda returns back to the startup manager page.

4. So relating to step 3 I put the AHT cd into the g4. I then connected the G4 to the G3 and went again to the startup manager on the G3 and I can see the AHT CD thats sitting in the G4 combo drive. I try to boot the disk and the same thing happens.

5. I have also tried just for kicks to boot the OSX install dvd from the firewire cd drive and it boots too.

In summary: I can boot another computer (g4) via the G3 in firewire. And when doing this I can see the "Test" drive which is connected to the G3 logicboard. I can even read and write and play music from the test drive!

But it just wont boot. I have tried other drives aside from my "Test" drive and they wont boot either.

I have never come across a problem like this before? Its quite unusual but exciting at the same time

Any thoughts?!

Jim