HDD: x2 Seagate 1TB (no RAID config at the moment)
PSU: 1200 Watt Cooler Master
Doing a build for a customer who needs a CAD engineering setup. The primary issue at the moment is the fact that all 16GB of ram posts fine, tests fine, works fine, however having all available slots populated with RAM causes the system to fail POST, the Mem OK! LED remains illuminated solidly and only if I populate the slots in an A1/B1/B2 with 3x 4gb sticks can I get it to post with the maximum workable amount of memory. Yes, I have tested all of the sticks in the A1 slot to see if they all post, they all are fine, I've also ran memtest 86 on all 16GB and no issues were detected.
Upon further inspection of the BIOS updates available on the ASUS website for this particular board, one of the updates (the first one I tried), 0801 BIOS version's patch notes described increased ram compatibility, so I flashed the BIOS with that version, still did not allow me to post the system with all 16GB of ram installed, upgraded to the 0901 BIOS, same issue.
This is the second motherboard that had exhibited these symptoms, so I've either somehow ran across a slew of defective motherboards or something's wrong with some setting or configuration in relation to this system.
A2 is only available to use when all four slots are populated since you can only use A1 for one stick, A1/B1 for two, and A1/B1/B2 for three sticks.