Hey there, try this:
1). Try cleaning out the DRAM slots on your motherboard, and make sure there's no dust inside.
2). Make sure the "ears" on the side of the DRAM slots are properly "unhinged", by pushing them outwards lightly.
3). Place the RAM stick on the slot, and press down -quite hard- on both sides of the RAM stick using your thumbs. Attempt to make the pressure even on both sides.
4). If the plastic sides of the DRAM slot completely cover the golden teeth on the RAM, your sticks are properly installed.
Cheers mate, hope this helps.