Disclaimer, the last time I built a computer it had a 56K modem in it.
I put this together with all of the recommended parts in the guide, with one change being a Supermicro X11SCA-F and 32 GB Corsair VENGEANCE LPX DDR4 RAM. I only have thee drives in at the moment, one 4TB for cache and two 16TB for media (third on the way for parity drive). There is also an NVME 1TB SSD.
Initially I was getting a heartbeat on the motherboard but it would not power up. Disconnected the JTPM1 cable from the front panel, it booted but gave me five short beeps one long. Took out one RAM stick and that went away.
Still no boot to BIOS.
Adaptec card has the Knight Rider red LEDs going and a slow flashing yellow.
Keyboard inputs create a chirp from the board, but nothing on the monitor connected via HDMI.
I figured out as soon as I hit submit that I need to connect via VGA.
Still running into the RAM issue. It will boot with a single stick in DIMM 2 or both sticks in DIMM 1 & 2. 2 & 4, 1 & 3, 3, or 4 all give a RAM error.
Tried to load Unraid and it’s stuck at the initial screen where you can choose the GUI. It counts down but never boots and you can’t select anything. There is a message quickly flashing that says something like file not found. I downloaded Unraid a couple of times with the same issue each time.
Only two things jump to my mind, and they are from personal experience. Since you know it will boot from 1 & 2, did you sequentially try each of the 4 sticks in DIMM 2? That would eliminate the RAM sticks as the issue.
In my case, I bought ECC RAM and my motherboad didn’t support it. But testing this way would still narrow down your issue to a bad stick or a bad DIMM.