Hi herryap,
Important :
Before installing or remove a stick of RAM, make sure to turn off the computer AND unplog the power cord. To prevent damage to RAM.
Have you tried to place a stick of ram in other Bank of Memory.
It is not forbidden to do so. Try with each stick of RAM, one by one, in each slot (bank of ram).
Maybe a stick of RAM have a problem. Like a bad insertion of RAM in Bank of Memory.
Each stick of RAM have a notch ( see your manual around page 16) so it can only fit in one direction.
So if there were one or more attempts to install the ram in reverse position, even just a little strong press on the RAM, is enough to cause damage to the RAM (at the contacts).
Maybe you have a problem with a Bank of RAM (Slot)
Remove a stick of RAM, check if in a slot, if he have a dust, scrap of paper or any small things.
Use a Flash Light, if needed.
Finaly when you inserted Check if a RAM are good inserted on slot.
The clips at both ends of the socket will snap (Normaly you Hear a sound like click), into place when the stick of RAM is securely inserted.
Gloup_Gloup