First try resetting BIOS to Optimal Defaults or its equivalent.
Then try putting in the black slots.
Then try each combination of 2 sticks in the A1 and B1 slots. Might find one of them is bad.
Then try clearing CMOS on the motherboard, setting Opt defaults, etc...
LOL yes, lots of fun choices there in BIOS. But shouldn't be anything that needs to be set to use all 3 sticks.
All computers need to be set to Optimal on first boot to clear any test settings.
Are the showing as 1600s? If not, need to compare default, and match BIOS to mem specs.
Asus manuals are always amusing about RAM voltage, point out nothing should use over 1.65, then all their approved RAM uses more.