Powerbook problems (Again - not trainz related as such)

Yep, the same powerbook, another problem. I did a work around for the trackpad, which has a faulty sensor, now another problem crops up and I am not sure of which.

My Mac has randomly been sleeping for no reason, which started today, I have been trying to find out why and I keep finding sensor overload temps in the console. Fine I thought, but it got into a loop where I could only keep the computer awake for a few minutes before sleeping.

Now I removed some ram, its fine atm with one, I've been swapping the same board from the upper and lower sockets to rule out the dreaded lower memory slot failure, seems to be fine, but I haven't plugged in the other yet as I haven't tested it.

Anyway, does anyone know what the symptons is for a lower memory slot failure or other issue? Either way, I know its going to be rather expensive.

EDIT: Its a dreaded 15" alloy model before anyone asks. Early 1.67ghz model