I'm going to have to let one of our other forum members take over from here, unless I can dig up more information. Although the symptoms do appear to match that of a Vreg chip fault, it does seem possible that the GPU could be at fault. If you push down on the heatsink assembly and it solves the issue, this would also say the GPU could be the problem. Maybe it's overheated and fractured the solder underneath, who knows. The fact you also said it appeared to be booting would be consistent with the GPU, a Vreg chip fault wouldn't start the machine at all.
If you do want to bake the GPU and see if it helps, I may be able to assist there... i've done some GPU reflow work on these iBooks as well. Ultimately you will need to remove the lower case and EM shield, then the top case, keyboard, the steel plate below the keyboard, the heatsink and fan assembly and possibly the LCD too. basically break the machine down until you can get clear access to the GPU, then just use the burning method as described above. I used a heat gun, but it took a lot more precision timing with the heat gun than the tea light method.
To answer your questions though:
1. It does seem more likely you pressed the GPU against the mainboard, especially if you pushed down on the heatsink. Since there's very little on the other side of the board from that, or so I can see, the GPU would have been the most likely component to "reseat".
2. The machine could kernel panic because of hardware faults, as in an incomplete connection with the GPU, especially if it's an intermittent connection in which sometimes it'll appear to boot, and others it may not.
Hopefully we should get some input from the other forum members soon as well, i'm getting pretty tired myself as I type this so who knows when i'll be back... i'll try to keep posted on the thread though and offer what I know.
If you do want to bake the GPU and see if it helps, I may be able to assist there... i've done some GPU reflow work on these iBooks as well. Ultimately you will need to remove the lower case and EM shield, then the top case, keyboard, the steel plate below the keyboard, the heatsink and fan assembly and possibly the LCD too. basically break the machine down until you can get clear access to the GPU, then just use the burning method as described above. I used a heat gun, but it took a lot more precision timing with the heat gun than the tea light method.
To answer your questions though:
1. It does seem more likely you pressed the GPU against the mainboard, especially if you pushed down on the heatsink. Since there's very little on the other side of the board from that, or so I can see, the GPU would have been the most likely component to "reseat".
2. The machine could kernel panic because of hardware faults, as in an incomplete connection with the GPU, especially if it's an intermittent connection in which sometimes it'll appear to boot, and others it may not.
Hopefully we should get some input from the other forum members soon as well, i'm getting pretty tired myself as I type this so who knows when i'll be back... i'll try to keep posted on the thread though and offer what I know.