This is most likely your RAM.
Remove your RAM and re-seat it, you should hear 2 distinct clicks when you press it in, after the clicks are heard give the RAM a little bit (not too much!) more pressure.
Also make sure that you're installing your RAM in the correct slots (A1 and A2 go together, B1 and B2 go together)
If you're only using one stick, put it in the A1 slot.