I would advise you to try to reseat the ram one at a time and log in to bio to check if the particular ram is being recognize.
In my case, I just bought a one kit 32 GB Cosair dominator 1866mhz (4 x 8 Gb) from amazon. the first time I insert the rams into my RIVBE , I noticed only 24Gb are being recognize. After troubleshooting one slot at a time I realised the first Dimm A1 isnt reading the ram. After a few tries,(taking out and reseating) I finally got my MB to read the 32GB of the ram kit.
Sometimes, the ram may seems to have seated properly but infact its not. Best is to reseat and check the bios to see if it is being recognised.
Also clear cmos if you have select XMP profile previously or the MB may not be able to boot up. Make sure all the 32Gb are being recognised before you select XMP profile.
Thanks Alaxang, I've reseated the DIMMS, and they all appear in BIOS. However, when I go to tools/ASUS DRAM SPD INFORMATION, dimm slots B_1 and D_1 read abnormal. I then switched the dimms around to see if the dimms in the abnormal slots were faulty, but I still read abnormal.