I just assembled this system and it has never POSTed. When I first turned it on, it immediately powered off, then powered back on by itself, then off and back on. The CATERR light is red, as are both DIMM indicators.
I've tried swapping the DIMMs and tried having just one in each slot. I also see the same thing if I power it on with both DIMMs removed.
I've tried all three BIOS switch positions, with no difference.
I've tried two different PSUs -- an XFX PRO 1250W and an EVGA Supernova 1000 T2. Same experience.
The CPU is an i7-9700K. The RAM is Corsair CMW16GX4M2C3200C14.
I don't have a different CPU or RAM on hand to test. What should I try next?