So it sounds like with the RAM disabled, everything works fine.
And with the RAM turned on, you get an error that the RAM is bad.
Could it possibly be... bad RAM? The system works fine otherwise, and with the board removed? Is this the model of board where the memory is soldered directly to it? Possible for you to replace?
I would go through all the obvious checks - clean connectors, no battery damage to motherboard, test with all expansions and other cards removed, triple-check the jumpers... but all else being the same, it just sounds like you've got a board with some bad RAM. It happens. Good luck!
