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DIY pc stuck in posting loop

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Mrzoom47

PCHF Member
Jul 26, 2020
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#1
I built a pc for my friend a month or 2 ago, and it was all working fine. Now, all of a sudden the pc will not boot. The computer posts and shows the splash screen, then the cpu debug light comes and the computer restarts. Oddly enough the only fan that stops is the cpu fan. Ive tried different ram, PSU, mobo, and booting drive and none of it works. Could it be a bad cpu? the pc makes it to the bios screen just fine and displays everything correctly. I tried reinstalling windows, and the usb drive i used got me to the windows install screen but just a min or so into the process the cpu debug light came on again and the pc restarted. Another peculiar thing, the vga light is on when the computer starts and the post screen doesnt show till 10 or so seconds after displaying an underscore in the top left.

My specs:
Ryzen 5 3600
G.skill Ripjaw 3200 2x8
500gb ssd WD blue (sata)
b450m pro-vdh max
evga 750 Watt 80 gold+ rated
zotac gaming 1650 super

Any help or advice would be appreciated
 
#2
Mrzoom47 said:
Oddly enough the only fan that stops is the cpu fan.
Click to expand...
This is your problem, the CPU is overheating and the system shutting down to protect the CPU from being fried.

Do you have the CPU cooling fan connected to the correct fan header on the MB which is at the edge of the MB, behind the CPU, next to the RAM.
 
#3
phillpower2 said:
This is your problem, the CPU is overheating and the system shutting down to protect the CPU from being fried.

Do you have the CPU cooling fan connected to the correct fan header on the MB which is at the edge of the MB, behind the CPU, next to the RAM.
Click to expand...

Yes, the cpu fan is connected to the cpu fan header and the temps in the bios read no more then 35c. The fan spins to full rpm, so im wondering how the cpu could overheat so quickly just on the post screen. How can this be fixed if it is truely the issue? Thanks.
 
#4
Can I ask that you do not quote every reply as I have to read the full post to make sure nothing gets missed,, thanks.

The CPU gets so hot that within seconds of being powered up you would lose the skin off your finger if you touched the top of the CPU.

Whether or not this can be fixed depends on what the issue is, a broken CPU fan is an easy fix but if the issue is with the MB then you are looking at a new MB or if still under warranty a repair by MSI or one of their approved agents.

I can 100% guarantee that this is the issue as the CPU cooling fan is not meant to stop turning until after the computer has been powered off and the CPU cooled down.

Has anyone been messing with the BIOS at all, changing the thermal parameters for the CPU cooler in the BIOS could cause such an issue.
 
#5
Well, the cpu fan spins up and keeps spinning through until after the post screen errors out and it restarts itself. Just to test i remounted the cpu and got into bios and changed the cpu fan to always run at full speed but same effect. Maybe i wasnt clear with my original description, but the pc never fully turns itself off, it just hard resets to a screen with an underscore in the top left. The cpu debug light comes on right at the start of powering it on, and comes on when it fails to make it past the post screen. Thanks for the support!
 
#6
That is a whole new scenario then as if it were a thermal issue the computer would not restart itself and then hang at an underscore, it would turn off and stay off.

If you can leave the computer sitting in the BIOS for a prolonged period of time the issue is definitely not related to overheating, if it restarts in the BIOS overheating cannot be ruled out.

Try a barebones set up outside of the case, the steps are below, please note that it is canned info and you only need to follow the steps that apply;

Best couple of suggestions I can make would be first remove the MB and do a barebones set-up on a piece of cardboard (make sure it is larger than the MB) only connect the PSU, the GFX card, screen, 1 stick of RAM and the keyboard.

IF your MB doesn`t have a power test switch you will then need to short out the 2 power on pins on the MB header to get the PSU to activate, you can use a small flat bladed screwdriver or a paper clip bent into a U shape, this is perfectly safe if you do not touch anything else, the idea is to see if we can get a BIOS screen if you do you can then add one component at a time until you find the problem component, you must power down and remove the power cord from the wall before adding another component, second suggestion try a known working PSU, it is not unknown for new components to be bad, third suggestion try and loan an ordinary PCI graphics card (not pci-e) again to try and get a BIOS screen.

Other things worth checking include, if you used stand offs beneath the MB are they in the correct locations (only where there is a screw hole in the MB) otherwise the MB will short out, check for stray screws or bared wires for the same reason, make sure the jumper cap that can be used for clearing the CMOS is not missing or on the wrong pins and finally try removing the CMOS battery for a few moments and then replace it, this will clear any possible bad MB settings.
 
#7
Alright, i stripped the pc down to just the cpu, one stick of ram, and graphics card. I used 2 psus to test, one known working for sure because my other system still boots up fine. When i power on my pc, im greeted by the VGA debug light and an underscore in the top left. After about 5 or so seconds, the light changes to CPU and it boots to bios. This is without my ssd connected. With the ssd connected, the pc makes it to the post screen, the spinning dot wheel comes up and then the CPU debug light comes on and system soft reboots back to the underscore in the top left. I dont think its the drive, because i tried reinstalling windows using a usb drive and the same issue arrises. Do you want pictures or videos of the situation to help troubleshoot better? Thanks.
 
#8
No pics or videos required thanks.

Can I just make sure that you had a keyboard connected while testing, POST will fail without one.

To rule out Windows or the device that Windows is on you could try booting from Linux on USB this uses the RAM to boot from, you will need to change the boot order in the BIOS so that the system boots from USB + on occasion secure boot needs to be disabled.
 
#9
Thanks for the advice, i went ahead and loaded ubuntu onto my usb drive using rufus and tried to boot from it. The only boot device connected being the usb drive. The pc started at the underscore again, with the VGA light on. Then, the debug light turned off and the ubuntu startup screen showed giving options like ubuntu, ubuntu safe for graphics, ETC. Anyways, no matter what option i choose or if i just stay in the menu for more then a few seconds the pc soft reboots again displaying the CPU debug light and returning to the underscore screen. Could this be a bad cpu? Is it possible that the bios can work just fine but for some reason an os cannot boot due to a faulty cpu?

I tried 2 different motherboards,
Gigabyte b450m ds3h
Msi b450m pro-vdh max

The gigabyte board wont even let me into the bios, however the msi board i can access the bios with no issue. Both motherboards try to boot and soft reset the same way, fans still spinning. Thanks for all the support, im new to the fourm :)
 
#12
If it helps, every other time the pc soft reboots it says, "starting automatic repair" then the cpu light comes on and it soft restarts. I originally thought it was a bad MOBO failing to load the drives or something but a second motherboard that is brand new did it too. Every part ive swapped out at some point even including the graphics card which i used an old gt 710 thats known working to test. The only part i havent tested is the CPU because i dont have another to swap. Is it worth it to get one from best buy and return it when im done or is something else the problem? And at that, would AMD cover this under the warranty? Thanks so much for all the help.
 
#13
If the CPU was bad you would expect problems from the outset.

When you tried Ubuntu had you first of all changed the boot sequence to boot from USB, disabled secure boot and was the USB thumbdrive in a black USB 2.0 port and not the blue USB 3.0 port type.

You are welcome btw :)

Just letting you know that I may be missing for a while, the year accounts need sorting so need my undivided attention :(
 
#14
Well, I populated a usb 2.0 slot on the motherboard, selected to boot from usb and disabled secure boot in the BIOS. Anyways, the ubuntu start screen showed and it had the options menu for launching ubuntu. But even just sitting in the menu itll error out the same way (black screening seemingly at random with the cpu debug light turning on) going back to the screen with and underscore in the top left and the VGA debug light on. The computer was working fine for months and this behaviour just randomly started just a few days ago now. Whats the next debug step, any other bios settings i should look for?
 
#15
Another note, the pc was turned on and running playing a game when it abruptly turned off and the behaviour started. Thats why i thought it was a problem at the hardware level.
 
#16
Mrzoom47 said:
The gigabyte board wont even let me into the bios, however the msi board i can access the bios with no issue.
Click to expand...
Are you aware that there is an advisory for the Gigabyte MB and the CPU that you have, if not, the advisory is that the board may need a BIOS update before a Matisse CPU will work in it, you can confirm this for yourself here

Got to disappear for a while now and do some paperwork, can I ask that if you reply meanwhile that you only post once and give me a chance to get back to you, I have up to 200 posts a day to get through so can do without any multi posts, thanks.
 
#17
Well the pc was working just fine with the cpu installed in that motherboard for months. Can a compatability issue randomly arrise? Also, I updated the bios to the latest version on the MSI board and still have the issue.
 
#18
Sorry but you never said which was the new MB so when you post "The gigabyte board wont even let me into the bios," it looked like that was the new board.

If you hadn't of updated the BIOS on the MSI board you could possibly have returned it, if it was just the Gigabyte board involved I would suspect a BIOS issue but to have the same thing happen with a second board I`m at a loss, best I can suggest and all that I have left is to ask a local tech to test your CPU, I`m not convinced that it is bad and you may just have been unlucky enough to get a faulty replacement board.
 
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