Inconsistent booting on Intel 5960X/Asus X99-deluxe

I just put together a 5960X node because 8 cores and AVX2 should do very well at electronic structure calculations (or anything using matrix-matrix and matrix-vector multiplication). I ran into a problem after it had run flawlessly for a day with half of the RAM. I added in the rest of the RAM (G.Skill Ripjaws DDR4 2400, 8 x 8 GB) and two more SSDs, and then it would no longer POST. After removing the drives and the RAM it was fine, but various combinations of the new hardware did not work, and the Qcode would stop at 00 (not used) or Ad (not even listed). I found out that I had routinely bumped the video card while putting in the RAM (this is not in a case, so nudging the card can lead to poor contact), and it was this improper seating of the vid card in its PCI-E slot that was causing the boot process to hang before getting to POST.