I've had a few repairs in this week. The first was a laptop that appeared to be completely dead, wouldn't turn on, no lights or anything. Charger was tested and working, so time to dismantle the unit. Inside I found the power socket was surrounded with hot melt glue, and this appeared to be a previous repair which had now failed. The power socket was actually in pieces and the central pin was no longer making contact with the board. I fitted a new DC socket and put enough of it back together to test it, and up it powered straight on.
There seems to be some possibly related problems around the power area, as it fails to successfully charge a battery. Either that or the two batteries I have tried are both duff.
Further investigation required.