But I have an important update, which is that I just realized that although the video card lights up and the case fan spins, the cpu fan does not spin.

I am definitely afraid that I might have damaged the board in some way, but could this also be a power related issue? 

Matt, looking at your video it appears as though you have the motherboard sitting loosely on the PC case. Are you able to confirm whether you have insulated the motherboard from the motherboard standoffs you screw the motherboard to? If not, then you could be shorting out the motherboard on the PC case.

I know it's a pain, but it would be better to take the motherboard out entirely and place it on a non conductive surface, I usually use cardboard, to bench test it.

Also, have you tried the video card in both PCIe slots? If not, try it. If the video card works in one and not the other, then you have a PCIe slot issue and need to RMA the motherboard. If it doens't work in either then you most likely have a faulty video card but would still recommend trying it in another PC even if it means taking it to a retailer to see if they can test it for you.

Thanks, I don't have easy access to another video card but at least you're giving me hope that there are more things I can try.

I also purchased a BIOS testing kit, since I'm pretty desperate. I have never used anything like this before... and it's not working at all. I posted a 3-minute video to help show the problem:

https://www.youtube.com/watch?v=_uJCrnASSs0

Looking back I'm realizing I may be totally misunderstanding the whole BIOS thing. I have always been a mac user and this is actually my first PC, so there are a lot of basic concepts I'm still trying to learn. After looking it up, I found out that the OS I installed (Windows 10) actually cannot load BIOS unless you perform a special kind of shutdown and restart from the Desktop. 

So is it even possible to load BIOS on this motherboard? I'm not entirely sure. One theory I had was that maybe the OS is installed only in the SSD. SO I detached it (after I took the video) and redid the same test with the BIOS testing kit with no SSD attached. Nothing, still no power going to the BIOS testing kit.

So I think the first step for me is to have a solid understanding of why this is happening. Some of the advice I've gotten so far has been related to my video card, but as far as I know, the video card doesn't even matter. When I first built this PC, before I installed Windows 10, I saw a config screen by turning the PC on with no video card and the HDMI connected directly to the board. All I'm worried about right now is being able to get to this point again (which I'm assuming is BIOS?) and then I'll start worrying about the video card again. 

Again I'm a total beginner so please correct me if anything I'm saying doesn't make sense.

I have a busy schedule so sorry I can't report back every day. Thanks so much.

Your first step is to eliminate any and all potential failed devices.  Strip it down to cpu, ram, and a known good .. meaning tested in another system... video card.. all properly hooked up.  Unplug everything else (excluding the cpu fan or cooler .. just stating the obvious here).  Disconnect hdd, any usb devices, any drives at all... See if you get a post message.  Then shut down and start hooking devices in one by one till it stops working.. that will be your indicator of what device you need to swap out.

I want to share another observation I made, but take it with a grain of salt because its based on a fuzzy memory from before the computer's video stopped showing. I thought that when I used to press the on button on the computer case, there would be a brief "whoosh" like a little surge of power, which you could hear because the fan would suddenly speed up a lot and then relax after a second. I might be making this up, but I think I noticed this also stopped right around when video stopped working. If this doesn't sound familiar to anyone lets just say I made it up, but otherwise, maybe its a clue to whats happening.

Here they are:

CPU: Ryzen 7 1700x 3.4 GHz 8 Core AM4 Boxed Processor

Memory: Evo Potenza 16GB 2x 8GB DDR4-2400 PC4-19200 CL 16 Diel Channel Desktop Memory Kit

Video Card: Radeon RX-570 ROG Overclocked 4GB GDDR5 Video Card

Motherboard: AB350M Pro4 AM4 mATX AMD Motherboard

Storage: 240 GB NAND SATA 3.0.6.0 GB/s 2.5" Internal SSD

Fan: Hyper 212 EVO Universal CPU Cooler

 

If you are describe your situation inaccurately it makes it very difficult to help you.