The first thing to check is that the CPU 4/8 pin power adapter is inserted properly.
Best to removes all devices including SSD and try booting with only 1 stick in DIMM slot A2.
If the PC successfully boots use A2 and B2 for dual-channel memory.
Here is the support page for your mobo you can also check your storage and RAM compatibility with
All good now. 8-pin Power cable was the first thing I checked before powering on; and It was out, so I plugged it back in to the PSU (and mentally crossed that off my list of possible problems for later). Apparently it falls out easily.
I can barely notice any gaming difference between this and my work rig(2970WX, 3070TI) on my preferred game settings. I also regret buying the H10 when they flooded Gumtree months ago when Intel announced its end-of-life. The mobo support for it is weak af. I never got the Optane cache recognised even with this "Optane/RST board partner" mobo. The next build I'm planning is all Maxsun/be-quiet! on whatever Ryzen ___X for B550M I can score a deal on.