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i5 8600K will not boot Windows with all 6 cores enabled


Hello all. This is my first post here, quite honestly because I've never had the need to do so. I've been working with computers for the last 16 years, professionally as Repair Tech for about 1, and various IT positions over the years. Anyway, long story short, did a new build sometime in the middle of March using the following components:

  • Core™ i5-8600K at 4.4Ghz
  • ASUS Radeon RX 480
  • 16GB Crucial Ballistix DDR4 - 2400 Mhz
  • MSI Z370M Gaming Pro AC mATX Motherboard
  • SSD OCZ 120 Gb
  • HDD WD Black 2 Tb
  • NZXT H400i MicroATX Case
  • PowerSpec 750W Gold PSU

Sorry, was easier to copy paste. Anyhow, at first, the computer ran fine, for about a few weeks before the first BSOD happened. Didn't think much of it, rebooted, went on for another few weeks. Started getting reboot loop, but again, it started working and did for about a week. So we're now at mid-may, when it started reboot looping completely. These are some of the steps I took to troubleshoot:

  1. Remove RAM, dust mobo, re-insert stick # 1 to Slot 1, no, stick # 2 to Slot 1, no. Slot # 2.... no, etc. Run memtest, OK. Not RAM.
  2. Connected an entirely new PSU. Nothing.
  3. Disconnect drives, case stuff, peripherals, boot from Windows 10 Install Flash Drive, no.
  4. Remove GPU, try on iGPU, no. Move GPU to PCIe# 2, no.
  5. Remove cooler, remove CPU, inspect mobo pins, blow, re-seat CPU, re-install cooler, no.

So after all these, I was left with 2 possible choices causing the issue - the CPU or the motherboard. So I went to Microcenter, purchased another Z370M Gaming Pro AC. Come home, rebuild the entire computer... boot - BSOD and reboot loop. # !@$# %^!!!!!!!!!!!!

In the years that I've been doing this, I have NEVER seen an Intel CPU that was never overclocked (I had it running at 4.3 Ghz [Enhanced Turbo Boost]), essentially new from factory, that was bad. Anyway, after a few failed attempts of entering BIOS(it will freeze the first 2-3 times when entering), I started messing around with CPU settings. I changed Number of Cores from ALL to 4. Save & Exit, system booted. Running. Ok cool. Went back to BIOS, upped cores to 5, system boots. Okay cool, cores to ALL, reboot loop again. Great. So I can still use my new PC at least for now.

So have I got a bad CPU? What's the deal? Also, at the back of my mind I can't shake the feeling that the VCore of this CPU is a little low. It's on Auto in BIOS, and currently, with 5 cores at 4Ghz, (manual clock multiplier of 40, I disabled Enhanced Turbo Boost), and the CPU VCore is fluctuating between 1.080V and 1.092V. My last PC that I've used for 3 or so years was running an Intel G3258 that was OC'd to 4.2 Ghz for the entirety of said 3 years. It was a champ, this issue is baffling me.

Update: I also tried booting Kubuntu 18.04 Live USB. With only 5 cores enabled, it works flawlessly. When I enabled ALL cores and try to boot, I will either get a Kernel Panic, a black screen, or the "OS loading" screen indefinitely. So bad CPU?

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3 Replies

Hello TheShotte,


Thank you for contacting us, I understand that you are experiencing system instabilities when all your 6 cores are enabled on your system.


In order for me to assist you better, please provide me with the .txt file that the System Support Utility will generate. To attach a file, you must click the "Attach" option on the bottom right-hand corner of the response box.


As well, please go ahead and stress and test your CPU through our Intel® Processor Diagnostic Tool and attach the results here, so we can look further into the functionality of your Microprocessor.


Here is the direct download:




I hope to hear from you soon.


Best regards.


Diego S.



Below is a direct Paste of the "Test Summary" tab of Intel Processor Diagnostic Tool 64Bit

--- IPDT64 - Revision:

--- IPDT64 - Start Time: 5/31/2018 2:12:28 PM


-- Testing


CPU 1 - Genuine Intel - Pass.

CPU 1 - BrandString - Pass.

CPU 1 - Cache - Pass.

CPU 1 - MMXSSE - Pass.

CPU 1 - IMC - Pass.

CPU 1 - Prime Number - Pass.

CPU 1 - Floating Point - Pass.

CPU 1 - Math - Pass.

CPU 1 - GPUStressW - Pass.

CPU 1 - CPULoad - Pass.

CPU 1 - CPUFreq - Pass.

CPU 1 - PCH - Pass.

CPU 1 - SPBC - Pass.

IPDT64 Passed

--- IPDT64 - Revision:

--- IPDT64 - End Time: 5/31/2018 2:16:18 PM



Also as per your request, attached please find my system information as per your System Support Utility. Also, for convenience's sake, I attached the results of the Diagnostic Utility test.


Hello TheShotte


Thank your response.


In this case based on the behavior of your system, and the replacement of the motherboard, we actually suspect that you are experiencing a hardware failure on one of the actual cores, so in order to isolate the issue, our best recommendation will be to replace the unit under warranty.


You can check the warranty of your unit here:


As well you can process the warranty directly through our live chat support, available from M-F 8:00 AM to 5:00 PM PST:


I hope this helps.


Best regards.


Diego S.