While version 0408 was where the new CPU became supported I see later version add more memory compatibility so be sure the BIOS is current. If the memory still isn't seen, reseat the CPU and RAM (I bet you already did that to the RAM.) Test RAM in all slots.
I upgraded from a i5 7600k to an i7 8700k. And I upgraded to an Asus prime z370-a motherboard. I kept the same ram which is Patriot Viper 2133 2x8gb. As soon as I upgraded everything I only had one stick of ram seated and it started up fine. I then realized it said I only had 8gb of ram so I checked and the other wasn’t seated. When I seated it it said my monitor did not have a signal. I have tried every combination of ram I could in different slots. Both sticks of ram work in one slot. But neither works in any other slot.

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