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[SOLVED] No POST after power outage

Apr 28, 2020
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Hello,
Today there was a power outage while I was playing and I cannot boot my PC again after that. I just upgraded my motherboard, RAM and cpu last week and it worked fine for a week. When I press the power button, everything seems to work properly, all the fans are spinning except I don't get anything on the screen, not even the BIOS so no POST as I have read on this forum. Also, I cannot shut down while maintaining the power switch button.
I tried all the steps of this guide (https://forums.tomshardware.com/threads/perform-these-steps-before-posting-about-post-boot-no-video-problems.1285536/ ) except the ones with the system speaker because I don't have one. I thought it was a problem with my new components so I tried to put back my old motherboard+RAM+cpu but same problem. The only difference is that I can shut down when maintaining the power button.
I also noticed that the USB ports at the back are not working. Noticed that because no light on my keyboard, then I tried to plug a phone and no charging. The ones on the front work (at least they charge my phone).
From that, my conclusion is that the problem is not my cpu, nor my RAM nor my motherboard. Therefore, it must be my PSU. However, all the fans are spinning so I don't understand.
Any ideas?

Full specs:
  • windows 10
  • motherboard: gigabyte B450M S2H
  • cpu: ryzen 5 3600
  • gpu: gigabyte gtx1070 G1 Gaming 8Go (2.0)
  • RAM: 2x8Go GSkill DDR4 PC4-28800 - F4-3600C16D-16GVKC
  • PSU: Corsair vengeance 550 M
  • SSD: intel 600 P series (nvme)
+ another hard drive 1To barracuda (full reference not relevant I think)

And the old components are:
  • RAM: HyperX Fury 2x8 Gb, 2133 MHz DDR4
  • cpu: intel i5-6500
  • motherboard: asus B150M-A/M.2
 
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Apr 28, 2020
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I finally solved it!!!! However it only worked with my new hardware (for the upgrade). I did a clear CMOS by removing the small battery from the motherboard. I had already tried it with another method which was described in the userguide of the motherboard but apparently it didn't work.
Also it worked with the old PSU so the PSU was not the problem!

Unfortunately, still no improvement with my older hardware. No clue why. I The only possibility is that there is a problem with either the motherboard, the RAM or the cpu. Maybe I did something wrong when I unmounted the cpu and cleaned the thermal paste. My main problem is now solved but I did find somebody who was willing to buy my old components but if they don't work...
 
Apr 28, 2020
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Sure!
Edit: I put the specs in the first message.

One other component that is common in my two tests is the gpu. Can it be a gpu problem? Even without a gpu, I should at least access the bios right?
 
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Apr 28, 2020
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Update: I tried today to change the PSU with one from an older computer which works. So the PSU should be a functionnal one. However, when I power everything on, the fans of the computer were all spinning but the PSU fan was not. And still nothing on the screen. I tried my usual screen connected on my gpu as well as another screen connected directly on my motherboard.
The old computer is not working well so maybe the PSU is the reason for that. I don't know if it's possible that my old computer was working with a PSU with no fan working. However it was still booting and my brother was plays league of legends on it. On my recent computer, no signal at all on any monitor.

Also, I found a third PSU in a box. It's the same model than the one from my old computer. I think it's a broken one but when I plug it into my recent computer, all the fans spin (including the PSU fan). Still no POST. So I think I already had the same problem once and used the warranty to get a new power supply and it solved the problem. Although the fans are spinning so the PSU provides some power but not enough or somehow not properly.

I am starting to get really confused. I would bring everything to a repair shop if possible but corona.
 
Apr 28, 2020
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Also one question in order to be sure all my tests are relevant: is it possible to plug the cpu power cable wrong (atx cable)? I have 4 pins on my ASUS motherboard and so I need to select 4 out of the 8. I see two square shapes and some pins are more rounded. I try to always align the square shapes from the cable with the ones on the motherboard.
 
Apr 28, 2020
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Well after a whole day of switching components, I think the problem comes from the PSU. When I put it in my old but functionnal computer, it doesn't boot.

However, putting the PSU from the old computer in my current computer doesn't help. But I think the PSU from the old computer is in a bad shape. The fan is not working and the old computer is working extremely slowly (probably because of the PSU). Still strange that my current computer doesn't boot with it.

I ordered a new PSU so I will see if it works. If not... well then I have no idea.
 
Apr 28, 2020
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The new PSU didn't solve the problem. I really don't understand now what it can be. It seems like my both systems (pcu+MB+RAM) are broken. Only one was mounted during the power outage. The only other thing common is the SSD drive which I tried to remove. I should get to the BIOS at least.
Also I am now trying to build the thing out of my case so it can't be a shotcut somewhere in my case.
I think I am going to bring everything to a shop.
 
Apr 28, 2020
8
0
10
1
I finally solved it!!!! However it only worked with my new hardware (for the upgrade). I did a clear CMOS by removing the small battery from the motherboard. I had already tried it with another method which was described in the userguide of the motherboard but apparently it didn't work.
Also it worked with the old PSU so the PSU was not the problem!

Unfortunately, still no improvement with my older hardware. No clue why. I The only possibility is that there is a problem with either the motherboard, the RAM or the cpu. Maybe I did something wrong when I unmounted the cpu and cleaned the thermal paste. My main problem is now solved but I did find somebody who was willing to buy my old components but if they don't work...
 

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