What causes bad memory slots on a new E-Machine EL-1352 motherboard

Hi,
I have purchased 3 new Re-man motherboards for my E-Machine EL-1352 SFF computer. Yesterday I placed a new motherboard into the computer case and both green lights were flashing. I shut it down and disconnected all internal parts except for the power supply and the processor / heat sink & fan. I had 1 long continuous beep shut system down. Placed 1 stick of memory into the memory slot next to the processor. Powered it back up and motherboard posted. Shut system back down and installed the 2nd stick of memory in the 2nd memory slot. Re-booted system it would not post, so I know that the 2nd memory slot was bad. This morning I booted up the computer to finish installing Window updates, but it would not post both green lights contentiously flashing. Again done a complete disconnection of all internal parts and replaced them one at a time. Still will not post. What can be the problem with this system
Thanks
Greg