Problem with H370M-ITX/ac

I just built a new server based on the H370M-ITX/ac motherboard, using an Intel Core i5-8400 Coffee Lake 6-Core 2.8 GHz CPU, SAMSUNG 960 EVO M.2 500GB SSD, and two sticks of Crucial 8GB 288-Pin DDR4 SDRAM DDR4 2400 for memory. Everything seemed to go well. I was able to install Ubuntu Server 18.04 LTS onto the SSD and after everything appeared to be working well, I started downloading the primary program that this machine will be running. After about 15 minutes of transferring about 50 GB of data from a local fileserver to this new machine, this new machine shut down. I can not get it restarted. I ran out of time to troubleshoot this on Monday night (the day I started this) so left it unplugged until today.

I initially thought it was a power supply issue, for a variety of reasons, so I pulled out an ATX PSU tester and it showed that the power supply was putting out all the right voltages on all rails. I then noticed that when "turned on", the power LED on my case was lit. I also noticed that on the LAN port that has an ethernet cable plugged in has a solidly lit orange activity/link LED but no speed LED lit. I do not see any LEDs on the motherboard like I've seen on other motherboards. I then noticed something that I found a bit odd... the CPU heatsink got pretty hot after a few minutes, which I find odd since it never booted up; none of the system fans ever turned on, including the CPU fan. I verified that the CPU fan does work by plugging the power to the CPU fan into another fan controller I had laying around. I had disconnected a keyboard and monitor on Monday evening, after installing the operating system and my plan was to just SSH into the machine, as this is intended to be a headless server. I just reconnected a monitor and keyboard and I get no lights on the keyboard light up. There is no video output to the monitor. I was hoping to see if I could at least get to the BIOS. I was hoping that if by chance, I had somehow burned out the CPU, the BIOS would at least tell me that. I was also hoping it would tell me if there was a problem with the RAM. Other than that, I can't think of what else to check. I have unplugged and replugged in everything. I have a power meter attached to the power supply, showing that when it is "turned on", it is drawing ~1.6 amps or 19.6 Watts. At this point, everything points to the motherboard failing somehow.

Unfortunately, when this was ordered from NewEgg, I had not saved all my packing material but I figured I may build another similar computer, so I ordered another motherboard. I carefully replaced the original motherboard with the replacement and put the original, back in a box so I can return in on an RMA. I can verify that the old motherboard was PART of my problem but not the sole problem. I can easily say this because it now shows the ASRock logo on the monitor and the instructions to press F2 or Del to enter UEFI Menu and a few other options in the lower right corner of the screen. I attached a speaker to the motherboard and there are no beep codes. All the case fans, including the CPU cooler turn on and slow down after a couple seconds, but still spin. While the keyboard lights up, nothing happens if I were to hit F2 or the Del button. Thinking I could have burned out the CPU too, I went to my local Fry's Electronics and bought a slightly inferior i3-8100, knowing it too should work. After changing it out, it makes absolutely no difference. As an interesting side-note, as I had previously mentioned the power drawn was ~1.6 amps or 19.6 Watts, it now draws ~1.9 amps or 24.1 Watts... this is with the fans spinning and the HDMI putting out the above-stated info. I have also tried switching around the RAM... each stick solely in each of the two slots individually, but still nothing else. Any ideas for what may be wrong?