Intermittent bootloop and BSOD

simonpking · 25 Apr 2020

Attachment 276170

My computer is intermittently getting stuck in a bootloop early on in boot sequence (just after UEFI BIOS settings option disappears with mobo logo and spinning dots). When it gets stuck in a cycle it repeatedly restarts, alternating between restart at mobo logo and 'automatic repairs'. It will occasionally freeze during these loops and need to be reset. Once every 20-50 restarts or so it will get through to windows. When it is in windows it will occasionally freeze or BSOD (with various reasons - see dumps), but sometimes run happily all day and be incredibly stable (like now when I'm posting this.) Some days it will boot straight to windows and be stable all day, but not very often.

Have tried new mobo, new RAM (though memtest86 on all RAM shows no errors), new PSU, reseated CPU, reset BIOS, updated BIOS, clean resintalled windows, it will also get stuck in the bootloop with no hard drive when trying to boot from usb win10 media. I have stripped all the way back to mobo, cpu and usb boot media and still get the problem.

The BSOD error messages arent' all captured in the dumps as I have clean installed windows a couple of times, but from memory they include:
IRQL NOT LESS THAN OR EQUAL
KMODE EXCEPTION NOT HANDLED
TRIED TO WRITE READ ONLY MEMORY
There were probably others too. Parameters and drivers are not consistent.

When stable, I have run prime95 (12hrs), intel CPU diagnostic, cystalinfo, furmark, HWInfo logging for multiple hours etc. None of these has shown any issues with hardware or temperature issues.

The only thing left I haven't switched out is CPU as I don't have a spare.

There seems to be no rhyme or reason to when it will bootloop and when it won't

Any help much appreciated.

Spec below:
CPU: intel i5-6600K
mobo: asus z270p
graphics card: nvidia GTX750 Ti
RAM: 2x corsair 8Gb DDR4 2133Hz 1.2v DS UDI (CT8G4DFD8213.16FA11)
SSD: Samsung MZHPV128HDGM
OS: Win10 1909 OS Build: 18363.778
PSU: Corsair CX600

MrPepka · 25 Apr 2020

In that case, the problem may be a broken cpu, have you tried to replace it with another cpu?

jdc1 · 25 Apr 2020

This is a poser.
I'd suggest:
- trying another CPU (as MrPepka suggests). If you don't have access to a spare, see if you can purchase one from a shop that'll let you return it for your money back if it's not needed
- run Driver Verifier (4 of the last 5 memory dumps were STOP 0xA): Enable and Disable Driver Verifier in Windows 10
- have a look at this link to see if it brings anything to mind: Hardware Stripdown Troubleshooting

simonpking · 26 Apr 2020

Thanks - will try another CPU. Bootlooped yesterday afternoon and then back to being ok this morning.
Am running verifier atm, will keep it on for 48hrs but so far no BSOD.
I have been through most of the tasks on the Hardware Stripdown Troubleshooting, but is still a great resource - thank you!

simonpking · 02 May 2020

OK - I think I've got to the bottom of it. As the consensus was it was a CPU thing, I started playing around with some of the CPU settings in BIOS (disabling turbo, hyperthreading etc) and through experiment it seems like the BIOS default core voltage was too low and causing instability (default was 1.136V). At 1.2V it is fine and has been stable with no issues for a few days.
Now it was originally at a higher voltage (as the CPU was overclocked) and only dropped to default when I reset BIOS as part of my troubleshooting process. So it turns out there is also another issue which caused it all in the first place, which is my Seagate 1Tb SSHD; I didn't list it in the spec because I knew it was on its way out so had removed it, but it is causing some very weird power issues; these issues seem to persist for a while post it being removed, but I havent' tested this too aggressively as I don't want to screw with the stable system I have now. When it is plugged in it causes boot issues even though it plays no part in boot. Cables are definitely ok (tested with another HDD). I was going to try to recover some data from it, but looks like that will be tough.