Got a new Asus Z87M Plus (BIOS 0703) with 32GB of Kingston HyperX Beast (KHX24C11T3K4/32X). Whenever I plug memory into slot A1 or A2, the red memory LED comes on and the board refuses to boot. I can put any two sticks of memory into B1/B2 and boot with 16GB RAM using just about any combination of RAM-related settings in BIOS, no problem. It does prefer to auto-detect the RAM as 1333 instead of 2400, but 16GB in slots B1/B2 always works. Any RAM in A1/A2 always fails.
Read some more postings, and found several who had problems with CPU sockets, coolers and so on. My missing info was i7 4770S CPU with a Cooler Master Seidon 120M liquid cooler.
I loosened the screws on the cooler and the spacers, also the screws that hold the motherboard to the cabinet. Popped out the CPU just to have a look for damage (found none) and put it back in. Now all RAM slots work OK, my guess is that the over-tightened screws caused tension in the motherboard or RAM sockets closest to the CPU.
Hope my mistake helps others with the same symptoms!