Riddle me this. B550M Pro4 won't post

I am at a loss and all my computer knowledge is put to the test with this issue so any suggestions from now on are kindly appreciated.

First of all specs

CPU: Ryzen 3 3100
Mobo: B550m Pro4
Memory: F4-3200C16D-16GIS by G.Skill 2x8GB
GPU: MSI GT 720
SSD: Samsung 960 evo 256GB
CPU cooler: Noctua NH-D9L
PSU: TR2 RX-450 (old I know but was working fine)

Build this system and everything run smoothly from the first go. No troubleshooting leds lighting up and posted just fine. Installed OS (WIN 10) no problem, configured some network stuff because I wanted it to be able to use remote desktop and wake on lan all good. Rebooted updated bios, set XMP and went to OS again all without a glitch. Downloaded A-Tuning and Ryzen Chipset drivers to control fans and set up ryzen power plan and then left the PC running. For two days all were good.

On the third I left the PC running and went on some errands only to come back to a blank monitor. The power led was on so I thought it went to sleep or something but after further inspection nothing was working. Pressed the button continuously for a hard shutdown, nothing. Opened the case and saw that two leds were lit. The DRAM and the CPU.

First thing I did swapped the PSU with another one I know it was working cause I am using it at my backup file server. It is old but I know it runs OK. I knew the other one was running OK too but just in case. Same behavior. Leds light up instantly no post.
Used third PSU from my main file server which runs flawlessly 24/7 No Post leds on

Cleared CMOS both jumpers and battery No Post leds on

took everything out to eliminate a short No Post leds on

Reseated ram to A1 B1 No Post leds on
Reseated single stick to all positions No Post leds on

Tried different stick from my main PC No Post leds on
Installed RAM on main PC worked on first boot and after a memtest 0 errors
Installed CPU and RAM on main PC, everything works and boots up fine

At this point I was sure it was a motherboard issue so I sent it back for a DOA. Two days later I got a response and images that the motherboard with their test CPU, RAM and GPU was running great. It posted and even booted into windows on first try.

At this point I am kind of at a WTF stage. I received the motherboard back, went to install all parts again and... No Post leds on

Tried my other CPU from main computer 3950X and also the GPU Quadro P2000 No Post leds on

Did the same with all three PSU's I have and No Post leds on

So I an now clueless and I have no idea what to do next, mind you returning the board is not an option since for some strange reason when it leaves the home it works.


No moving house is not an option and yes I did try it on different wall outlets that run on different circuit. Even powered it through my UPS but nothing.

Any suggestions would be more than welcome.

Thank you for your reply and your suggestions unfortunately I have tried all those as well.

No peripherals, no sata, no headers, even no fans since the heatsink of the cooler is enough to cool this CPU passively on idle. Tried booting with m.2 and without still no luck. Reseated CPU just in case but still, no post and the leds are on. not even using a power button just shorting the headers.

Swapped vga cables for dvi, swapped all power cords from all three psu's nothing.

I have a speaker that I have connected to the headers and it doesn't make any sound and this is weird, (did swap orientations just in case I am placing it wrong) but my assumption is that the default setting on the motherboard is to have it disabled. I can't check it though.

So again I am at a loss.

I have a weird reasoning to my head, maybe this board needs a more powerfull PSU the max wattage I have tested is 550 but this is just crazy talk of a frustrated guy.

I will, once I get my hands on one but it is
highly unlikely. I mean those specs could get
away with a much less powerful psu.
plus it did work for a while with no issues.
If it needed more it would from the beginning.

Hello again,

Let me share the root cause of this issue.

First, I doubted memory(G.skill) as I wrote in the last reply.
I bought it at famous PC parts shop, so brought whole PC in the shop and tested it.
G.skill memory worked well on the shop's test PC and other memory didn't worked for my PC.

I asked another shop to check my CPU(Ryzen 5 3600), and finally they found it was broken.
They sent me new CPU and now my PC successfully started again!

MadScientist wrote: Could be the PSU. I would try a PSU with at least 650W.

a bunch of bs.
even moderately overclocked intel 10900 with 2080ti on full load won't draw more than 550w of power.

With OP set up it is probably around the 200w on full load

450w PSU assuming it is close to it's true rated power would be more than enough

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