Hmm ok. I wonder if it's because you "only" have 4GB of ram.
However going through your manual - it states you should put the ram in the blue slots for max OC ability (if you plan to do so).
One last thing - have you tried setting the CAS latency of your RAM? Also - what exact model number is your RAM? You should set them to the manufactuerer's specifications in your BIOS.
One more thing you mentioned your ram is 1866 - however I can't find that exact model...the closest one I found was Patriot G2 1600Mhz 2x2GB. I know the A8's are highly sensitive to RAM since they use it for the igpu as well.