Windows 10: Why is my computer Soft rebooting, and crashing?

I got this pc built a year ago. I went recently to get the Hardware checked since I got a critical error related to hardware. The store said there was no hardware issues so then the other idea was a software issue. So i reinstalled windows and downloaded the bare minimum of Steam, discord, Logitech hub, and one game Helldivers 2. The issue still persists. These 2 links are the 2 events that occurred after the screen turned black and then rebooted up again. I did a command prompt scan now and no issues were found, and there are no alerts from windows security. Loss of power could be my power su

:)

 

all games crash!

ive watch my temps and both the cpu and gpu are within normal ranges. when it freezes it simply freezes the image and stops the sound. i must reboot to get back to windows.

 

all games crash!

I suggest you run rthdribl > http://www.daionet.gr.jp/~masa/archives/rthdribl_1_2.zip
Increase the window size step by step and watch your vga temps permanently.
What happens?
If it crashes, run at stock speeds as suggested before and retry.

P.S.: When your system locks, does the display signal turn off after a time?
Stuttering sound or no sound at all when freezing?
What X1800XT model do you own exactly?

 

Repeated Crash-rebooting on Windows 10 - what hardware is at fault?

Brief overview
About a couple weeks ago, my custom-desktop (built 2015) started hard crashing and auto-rebooting. The computer has crashed so many times at this point that I can barely keep track (like 50 times in 2 weeks). When I start it up in the morning, it works fine for a few hours, then it will suddenly crash, reboot, and then wait 5-10 min before crashing again and starts to enter the death-spiral of repeated crashes that become increasingly more frequent. Last time this happened (yesterday), it couldn't even get past the BIOS splash screen before another crash. Seems like a short circuit? I have tried a lot of troubleshooting steps so-far, and will list that out in detail below - but for those TL;DR, I am 98% sure it is hardware related, the question is, how to isolate what piece of hardware is at fault? How to test? motherboard or power supply or something else?

Computer Specs:

PS: EVGA 750W GOLD Power Supply

MB: Asus Z170-A, running American Megatrends BIOS 3802 3/5/2018 (UEFI)

CPU: Intel i5-6600K Skylake CPU @ 3.50GHz, 3504 Mhz

GPU: EVGA NVIDIA GeForce GTX 980 Ti

Troubleshooting steps taken thus far:

1. I dis-enabled auto-reboot (per suggestions online), and then when machine crashed again, it automatically rebooted, which clearly seems to indicate that the problem is not triggered by Windows.
   
2. I checked the Windows Event Viewer, and here is what it looked like:
   Kernel-Power Event log
   There is no detail available beyond this event ID, because the machine apparently doesn't have a chance to write a dump file prior to crashing, which strongly suggests that it is a hardware problem. The crashes happened several times with no software running, so that confirms that hardware is likely suspect
   
3. I opened up machine and thoroughly cleaned it and checked pin connections between power supply and the motherboard. I re-seated these connections, and it seemed to stop the crashes for 5-6 days, but then it started happening again.
   
4. I updated BIOS to most current build available
   
5. I installed a CPU temperature reading program to see if the i5-6600K is overheating. Here is a normal read-out (cold start)
   CPU Temp cold start
   followed by a read-out I was able to capture shortly after a crash. I don't know about you, but 57°C seems awfully hot for a processor. Makes me start to think that the processor is overheating? Which gets to the next thing
   CPU Temp after crash
   
6. I have tried tweaking the BIOS to disenable overclocking but I am thus far unsuccessful - I don't know why the ASUS Z170-A motherboard is so hard to throttle down, the 'EZ menu' doesn't provide an easy option to just shut it off, and in Advanced mode, even with most settings in the 'AI Tweaker' panel disenabled, it still overclocks. Still looking for a good guide out there that can show me how to do this.
   

Can you provide any insight? I am at my wits end