X370 Killer SLI/ac won't POST

I downgraded the BIOS but that didn't fix it.

I looked into the program that you recommended but it just suggested the same timings as the ones given on the packaging.

The problem is still though, that it's almost certainly not an issue with the RAM. The exact same set of RAM is rock stable on one board with the same BIOS, same chip model, and unstable on the other board with the same BIOS, same chip model. Both boards are the exact same model.

Could it be drivers? The symptoms are many and varied BSODs but it's clear that clocking the RAM to 2400 creates stability, so it shouldn't be anything on the hard drive.

I RMA-ed the board and got a replacement.
The replacement POSTed immediately.

So that's good. Now I have another problem.

The RAM I have for both builds is G-Skill FlareX F4-3200C14D-16GFX.
I have the BIOS on the second machine as v3.50 (the first machine has 3.40).
On the second machine, setting the RAM to its XMP profile (CL 14-14-14-34, 1.35v, as listed on the package) results in serious instability and constant BSODs. Setting the RAM to the 'default' of 2400 appears to be stable.

I have tried swapping the RAM between systems, and as far as I can tell, it's not the RAM. The same problem happens to the second system when I put the (identical) RAM from the first system in the second system.

Not sure why this is. The BIOS v3.50 should definitely be able to handle the 3200 speed RAM. The first system has been steady at 3200 speed, and it has BIOS v3.40.

I don't think it's a driver issue, since the BSODs are pretty random types, all over the place.

Sorry, yes. Mistype. The right lead is going to the CPU. I know the difference between the two.

Ok, I have a new problem. I am starting on the second Ryzen build and again I'm running into a lack of POSTing. The specs are the same but recall from above that when I tried to get the first system to POST, I ended up swapping out the motherboard and using the second x370 Killer SLI/ac motherboard I purchased.

Now I'm trying to get the second system to POST, using the first motherboard (which never POSTed successfully, although the second one did).

So the current status is:
Known good RAM (I used it to POST the previous Ryzen build).
Known good power supply
Known good GFX card (ASUS NVidia GTX1060)
Known good monitor on HDMI

The only two unknown pieces are the Motherboard and the chip.
I checked the chip for bent pins.
I have the 24-pin and 6-pin connectors securely feeding power to the motherboard.
I have a 6-pin connector securely feeding power to the GFX card.
I have cleared the CMOS after inserting all the pieces.
I have the RAM in the right place.

I have waited upwards of 30 minutes at a time for POST with no luck.

I think the only thing left to do is RMA the motherboard, yes?

We made it work. Couple of things it could have been:
1) a hard drive needed to be plugged in?
2) First POST takes a long time and I was never patient enough. I may have accidentally left it on long enough one final time and I came back to the room and it had posted.

Thanks!