So the memory expansion card is giving some grief. But it might or might not be the chips on the card.
The card looks new, so it might be the card, or it might be the connector. My next suggestion would be to try cleaning the edge connector on the motherboard, and give it a good clean!! The other thing to try is pulling the card back ever so slightly off the edge connector.
So you could try cleaning the edge connector, or mounting it a little out from its "perfect seating position", or you could try keeping the card disconnected/unplugged and now start testing the motherboard bare bones with some software.... try loading Workbench and see if it will sit idle overnight. Load a game and see if it will sit at the title screen overnight, etc.
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Just to clarify for me, if you remove the hard drive and run the ram test again, will it give errors? or is it only when the hard drive is plugged in??