Powerbook 867 MHz blacking out

Hi, and thanks for providing the answer to any questions I might have had during the last two years of nearly problem-free Powerbook ownership.

However, for the last few days I have started having some more serious problems. My 12" 867 (10.3.9, 640MB RAM, Toshiba MK4021GAS 40G HDD), will suddenly black out if subjected to any kind of knocks or movement. If I treat it as an egg, no problem, but if I move it too fast, the screen goes black (sometimes first with the backlight still on, and then dies completely). Same thing happens while it is sleeping; move it too fast, and the indicator light goes out.

When this has happened, it doesn't reboot immediately when I push the power button, so I'm not sure whether only the screen or everything is dead. Once during reboot, I had a short flash of colours before normal booting continued, so maybe there's a problem with the video card or cable, though screen angle or movement has no consequence. I thought maybe the HDD could be the cause, but as it works fine as long as it's not moving, could this be it? S.M.A.R.T. status says verified, though.

Anyone have the solution to this?

Yup. Thought of that, because I had to change my battery a while ago, and have been changing between them once in a while. None of them fit perfectly, so that might be causing it sometimes. However, it does the same while running on mains power only, with no battery.