I had already taken it apart and made fresh connections in HD cable, processor daughter card and ram card - along with the interconnect cable between the two halves, obviously.

Good advice on the battery, though, and it could well be that a dead main battery is part of the problem. And there are indeed video artifacts when the battery is completely flat.

The main battery does take a small charge, however, and that could explain why if it isn't left unused, it boots up fine. However, when the machine is misbehaving, it won't power on etc. even with the main battery out, so one suspects that there are further issues....

Is there a GLOD-equivalent on the 1xx-series?