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PC suddenly turned off and now only boots if 1 CPU core is enabled

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Tynan

PCHF Member
Apr 7, 2023
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#1
Hi, my PC which I built about 7 years ago suddenly turned off while I was watching YouTube. When it turned back on it said it was "preparing automatic repair" but it kept restarting before it even got to the windows logo. I tried to run Windows installation media from a USB drive but it would just restart every time the Windows logo appeared. I was able to access the BIOS settings so tried running with only 1 core enabled (out of 4) and my PC booted up like normal and works just as it did before (but slower). I tried it with 2 cores enabled but the same problem occurred.

So is my CPU damaged or could it be something else?

CPU intel i5-6600K
Motherboard MSI Z170A Gaming M5
Power Seasonic 620W
RAM HyperX 16GB DDR4
Graphics AMD R9 270
 
#2
Hello Tynan,

First thing I suggest you do is stop messing with the CPU cores before you brick the CPU.

The following requires the computer case to be opened so take the following safety precautions 1st, disconnect the power cord from the wall socket, press the case power button for twenty seconds or so to get rid of any residual charge in the system, take anti static precautions before touching anything inside, you can do this by touching a bare metal part of the case or PSU.

Remove the add on GPU from the MB, put the side back on the case, connect the screen to the appropriate video port on the MB, hook up the power cord and the keyboard, restart to access the BIOS and do the below;

Restore the MBs default factory settings in the BIOS, they are sometimes listed as one of the following " factory defaults" "most stable" or on newer boards "optimized" please note that if you have both the "most stable" and the "optimized" options in the BIOS you should choose the most stable" option as in this instance the "optimized" settings are a form of overclocking that can cause instability.

Save the new settings, exit the BIOS, restart the computer, test by using the computer as you normally would, unless you have a question only post back with an update once you have done all of the above.

Good luck..
 
#3
Hi, thanks for your reply. I had already tried another GPU and I did set the BIOS back to default settings. I removed the CMOS battery, disconnected all USB devices, all the HDD and SSDs and it still wouldn't boot the Windows installation media from a USB drive. I also could not get into safe mode.

I did try your suggestion though and I had an odd problem. When I took the GPU out I would get no signal from the motherboards HDMI connection. The BIOS is set to use the integrated graphics. I put the GPU back in and then I would get a signal from the motherboard and not from the GPUs display port connection. I again removed the GPU and again there was no signal from the motherboard.

I tried it once more but this time I disabled the CPU cores again and it worked. I get a signal from the motherboard and there is no GPU installed.

There is a simple option in my BIOS to enable either 1,2,3 or 4 cores, could this really damage my CPU.

I also just remembered that there is some debug LEDs on the motherboard. (Can't see them when there is a graphics card installed) and when I try to boot with all cores enabled the first digit reads 0 and second just rapidly flashes between numbers. ( possibly 2 and 8). According to the motherboard manual all codes beginning with 0 are to do with "Power on CPU/North bridge/South bridge/ cache Initialization.

I think the problem has to be either CPU, MB, or maybe power supply but I don't have any spare parts to test.
 
#4
Have you restored the default factory settings in the BIOS as was suggested, clearing the CMOS by removing the CR2032 batteries does not always work.

Tynan said:
I did try your suggestion though and I had an odd problem. When I took the GPU out I would get no signal from the motherboards HDMI connection. The BIOS is set to use the integrated graphics.
Click to expand...

If you did as was described there would be no add on video card detected so the onboard video would be the default.

In case not already aware, the onboard video comes from the CPU and not the MB so when you mess with the cores you mess with the video.

Suggests you start with a clean slate and do exactly as was post in my reply #2 and go from there, the non booting media and not being able to get into safe mode are separate issues from the video issue and the two need to be addressed one at a time and starting with getting the hardware itself stable if we can.
 
#5
Yes I did restore to default settings through the BIOS. Sorry for the confusion. I just mentioned the CMOS and the removing of HDDs to show that I did all the usual steps I found online to fix the problem. Disabling the cores was the last thing I tried and just by pure chance.

I also did not make it clear that the PC was not booting when the GPU was removed. I tried your steps again just to double check and I'll write down exactly what I did.

The PC was running with one core enabled, I shut it down and removed the GPU. I turned it back on and was getting a signal from the integrated graphics.
I went into the BIOS and restored it to the default settings and restarted PC. When it restarts I get no signal from the PC and it is not booting up.
I put the GPU back in and it's back to the "Preparing automatic repair" loop.
 
#6
Tynan said:
I put the GPU back in and it's back to the "Preparing automatic repair" loop.
Click to expand...

Possibly a video or a chipset driver issue which while a pain in the proverbial unlike and not as much as disabling cores ( which you should not need to do in any event ).

With the MBs default settings restored and the GPU in the PC see the below;

See if you are able to force the computer to start in the Windows Recovery Environment (RE) by starting up and shutting down the computer two or three times using the case power button, please note that you need to shut down the computer after the MBs splash screen and just before Windows attempts to load, if successful you should then continue to the Troubleshooting options and then hopefully be able to use Reset this PC, a system restore point or Safe Mode etc.

When you post back with an update, can you let us know if the RAM is two 8GB sticks or a single 16GB stick.

Highlighted as it is important, while you have the PC functional/before doing the above can you make sure that the Windows Power Plan is set to Balanced and not High or Ultra Performance.
 
#7
I've tried entering Windows Recovery Environment but it does not start. My PC was on high performance mode though, I thought it was on power saving. I've changed it to balanced but I still couldn't enter RE.

I have 2 sticks of RAM, I've tried them individually and in different slots. I ran memtest86 and got no errors. Memtest would only boot from USB drive if I disabled cores.
 
#8
What speed is the RAM.

Try inserting just the one stick of RAM in slot two, the second one away from the CPU.

Tynan said:
Memtest would only boot from USB drive if I disabled cores.
Click to expand...

What colour USB port did you have the USB device in.

If you are using a USB type keyboard, make sure that it is in one of the black USB 2.0 ports and not one of the faster red 3.1 ports.

Restart the PC, enable all CPU cores in the BIOS, restart and see what happens.
 
#9
RAM is 1333Mhz.

I inserted one stick of RAM into slot 2 and used a regular USB slot on the back ( I was inserting it into a blue USB 3 slot on the front) I have noting in the USB 3 slots now.

Memtest did start but it froze after 30 seconds. I tried it 3 times. It also did not run smoothly when it was working. It would freeze for many seconds then run again. When it froze I left it for at least 20 min to see if it would start working again. I also switched the stick of RAM I used.
 
#11
Oh sorry it's 2666Mhz.

It took a long time for Memtest86 to boot. I got a black screen after the MB logo for many minutes. When I first tried memtest I did not wait that long on a blank screen before I assumed it was not working and turned off or restarted PC.

I will try it again in a USB 3 and see if it will boot.
 
#12
Tynan said:
Oh sorry it's 2666Mhz.
Click to expand...

The RAM is not appropriate for your CPU, Intel state here up to 2133MHz and if you have XMP enabled the RAM will get auto OCd past what the CPU can handle and the PC fall over.

Tynan said:
I will try it again in a USB 3 and see if it will boot.
Click to expand...

Sorry but was neither what was suggested or asked.

phillpower2 said:
So the behaviour changed when you enabled all cores and put the USB device into a black USB 2.0 port.
Click to expand...

Older MBs like the one you have do not have USB 3.0 or 3.1 drivers mapped into the BIOS chip only drivers for up to 2.0 so you100% should never have a USB type keyboard connected to one of the faster ports and likewise you should never try booting from one of the faster ports either, disabling secure boot in the BIOS also needs to be done when trying to boot from a USB to either install Windows or run a diagnostic tool.
 
#13
You can run faster RAM with the Z170 chipset motherboard. I did not change the RAM, MB, or CPU since the original 2015 build. I have not enabled XMP in the last few years.

I did not know you should not boot from USB 3.0. Memtest did the same thing anyway. I tried Windows installation media again in the 2.0 port but it had the same problem. The keyboard was never connected to the USB 3. I don't have secure boot enabled.
 
#14
Tynan said:
You can run faster RAM with the Z170 chipset motherboard.
Click to expand...

Yep but only if there is a processor in the board that can handle faster RAM and there is only the one, the fastest CPU compatible with your MB is an i3-7350K which can handle a stock RAM speed of 2400MHz and as if by coincidence the fastest stock speed of RAM for your MB is 2400MHz meaning that anything faster has to be OCd, MSI could say whatever speed they like is compatible with the board because there is no way of disproving it without a CPU capable of handling any claimed speed.

Tynan said:
I have not enabled XMP in the last few years.
Click to expand...

Which kind of reinforces what has been said, you didn`t purchase XMP capable RAM to just not use the feature did you.

If you have access to another PC and a spare flashdrive, download a live Linux Distro and boot from that, Create a bootable USB stick with Rufus on Windows

If in Ubuntu the PC 100% works with all cores enabled the CPU, MB and RAM are most likely all good.
 
#15
Not sure if I understood the instructions correctly but here is what I did.

I got Linux lite and used Rufus to create the bootable USB stick. I get the initial start-up options but when I launch Linux I just get a blank screen.
I also tried Ubuntu and I also get the initial options but after I select "Try or install Ubuntu" I just get a blank screen.

I left them on the blank screen for over 15 Mins. I tried Ubuntu again on the one core and it boots and runs fine.
 
#16
Tynan said:
I left them on the blank screen for over 15 Mins. I tried Ubuntu again on the one core and it boots and runs fine.
Click to expand...

That does not bode well for your CPU.

When you tried Linux/Ubuntu did try it with just the one stick of RAM in slot two, the GPU removed and using the onboard video and had you changed the boot sequence so that the BIOS booted from you USB device.
 
#17
Yeah I tried but still the same. At least I can run it on the one core until I get a new PC.

Is there any possibility that there could be a fault in the power supply and it can't supply enough power to the CPU when all cores are enabled?
I'm not getting my hopes up!
 
#18
I was going to suggest that you ask around to see if you can borrow a known good 500W Bronze efficiency rated PSU to swap in and test with, this with only the onboard video an no add on GPU in the board, if the problem still persists the MB is the most likely culprit as under normal use a CPU is less likely to fail than a MB is.

Other than the above we are stuck as we can`t test your CPU without having all four cores enabled
 
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