Unknown problem with ASRock AB350 Pro4 build

[freejester]

Before anything else, here's my part list:

mobo - ASRock AB350 Pro4 AM4
psu - Seasonic G Series 650
cpu - Ryzen 5 2600X (not installed, see below)
gpu - Gigabyte RX 580 8GB Aorus
ram - G.Skill Flare X Series 2400, 2 x 8GB

I've got a Western Digital Blue 2TB HDD, and a Corsair Force MP500 M.2 2280 120GB SSD, both already installed.

I already know the CPU isn't compatible with my motherboard out of the box. My dad is doing a build at the same time as me with an ASRock x370 Pro4 and the same CPU, so we've got the BIOS update kit with an AMD A8 9600. He successfully updated his BIOS, and has switched to his 2600X with no problems. I've installed the A8 9600, but I'm not getting video out and my peripherals aren't getting power (no numlock light). So I'm stuck before even updating my BIOS and using my actual CPU. When it powers on, the lights in my video card turn on and fade a bit, then cut out abruptly and restart. The fans continue to run normally. No beeps, the monitor doesn't even wake from sleep.

I've tried booting without ram, and with each individual stick in each slot. I've tried the video card (HDMI and DVI), and onboard video out with the video card disconnected. I've tried different monitors and different keyboards (USB and PS/2).

I still can't get the gosh darn thing to boot. It powers on, fans all spin up fine, but it just stays like that. It does turn back off when you hold power, I don't know if that's relevant.

I'm really at a loss. Any help would be appreciated, thanks for reading
-Jackson

 

[drivinfast247]

Make sure ALL power cables are attached to the motherboard. Especially the forgettable 8 pin. Then remove the GPU and plug the display directly to the motherboard.

Also do what the guy below said and reset the BIOS.

 

[drea.drechsler]

for just updating the BIOS, I'd definitely use the APU alone for video. Be sure to remove the RX580, of course.

do you have a speaker to connect to the speaker pins on mobo? beep codes help.

first double check all connections

Try with one stick of RAM, then the other.

you might try resetting cmos: with the pancake battery removed, short cmos reset pins 15-30 seconds or so then reassemble and try it

then probably the worst: if it's assembled in the case you may need to remove it. One of the most common mistakes on assembly is a few missing standoffs that allow the board to contact the tray, or an unused standoff that should have been removed doing the same thing. Bench-testing it first would help you isolate any problems that assembly in the case causes.

If all else fails: you could swap parts with your dad's in case something's at fault: power supply would be something to swap out.