I'm at a bit of a loss with some computer issues I've been having. After not using my PC for a week or two, it suddenly would no longer boot up. Pressing the power button did nothing. After opening it up and reconnecting some wires, the system fired up but simply shut off within minutes. This problem has persisted for 2 weeks now and I'm suspecting it's the CPU even though that is supposedly one of the least likely parts to fail. I would really like some input on this as I'm pretty desperate at this point and would like some more certainty before contacting Intel for an RMA.
The specs: i7 7700k, MSI Z270 SLI Plus motherboard, KFA2 FTX 1080 GPU, Corsair Vengeance LPX 2x8GB RAM, Cooler Master v550 PSU, Samsung Evo 850 SSD.
Things I have tried: - Different outlets around the house and another power chord
Cleaned the case and components with compressed air
Replaced the PSU with a brand new one (Corsair RM650x) as well as all internal power cables
Reset the CMOS, removed mobo battery and updated the BIOS to the most recent version
Tried all possible RAM configurations (just 1 stick, both in different slots...) as well as 2 new modules (G-Skill Ripjaw V)
Replaced the entire Motherboard with a brand new one of the same model
Reconnected all components, reseated the CPU and reapplied thermal paste
Replaced the GPU with a friend's Asus GTX 970
Ran the system without the GPU connected and just on the integrated graphics (this seemed to work but after having the system crash with the GPU and immediately removing it, it shut down again even on the iGPU)
Ran the system without the case power switch / reset cables attached to rule out faulty wiring
Idled in the BIOS screen after a crash without even the SSD/HDD with the OS on attached
Did several stress tests such as AIDA64 and OCCT as well as a variety of Windows and 3rd party diagnostics tools (the PC either crashes or diagnostics comes back clean)
Monitored the system with MSI Afterburner and checked logs to rule out temperature issues (highest temp recorded was 72° in the CPU after extended stress testing at 100% use)
Checked Event Viewer (nothing in particular stands out)
Tweaked Windows power settings, disabled fast boot, disabled restart on failure
In other words, I've replaced all components other than the CPU (temporarily, just to see if the system still crashed) including the PSU, GPU, Motherboard and RAM. I've verified that the crash happens even in BIOS without an SSD with the OS on attached. The CPU seems to be the only possible culprit here, and this seems confirmed by the Intel Processor Diagnostics Tool always crashing the system during the stress test / check. It seems that the system runs stable after not being used for a few hours up until it comes under load. When it then shuts off the first time, it often doesn't make it past BIOS again or will crash just idling on the desktop when you reboot it immediately after.
I'm planning on having it RMA'd by Intel but am still baffled by what might be causing this. I've been suggested to try running it with hyperthreading or certain cores disabled so I might still do that first. I've done a fair bit of searching and didn't find much that compared to my experience other than this guy who had the issue fixed with a new CPU. Any thoughts or input would be greatly appreciated.