So I just recently upgraded from a i5 7600k to the i7 6800k (needed more cores).  I do a VERY humble OC on the 6800k by 4.0 ghz with everything else set to auto, stress test for 6 hours with a super stable result.  Two weeks later, I wake up my computer from sleep mode and I get a rude BSOD with no indicator of what caused the problem.  I do a hard reset and it refuses to POST, just cycles then gives me that sweet FF with at CATTER LED lit.  Thought it was the mobo but turns out it was the CPU.  Thank goodness I was still under the 30day return policy so I just swapped it out.
 
My question would be, what caused that fatal error?  Could it have been the OC?
 
Heres my build:

PCPartPicker part list: https://pcpartpicker.com/list/z39Nbj
Price breakdown by merchant: https://pcpartpicker.com/list/z39Nbj/by_merchant/

CPU: Intel - Core i7-6800K 3.4GHz 6-Core Processor (Purchased For $350.00) 
CPU Cooler: NZXT - Kraken X52 Rev 2 73.1 CFM Liquid CPU Cooler (Purchased For $152.00) 
Motherboard: EVGA - Micro 2 Micro ATX LGA2011-3 Motherboard (Purchased For $205.00) 
Memory: Corsair - Vengeance LPX 16GB (4 x 4GB) DDR4-2400 Memory (Purchased For $158.38) 
Storage: ADATA - Ultimate SU800 128GB 2.5" Solid State Drive (Purchased For $50.93) 
Storage: Samsung - 850 Pro Series 256GB 2.5" Solid State Drive (Purchased For $90.00) 
Storage: Seagate - FireCuda 1TB 3.5" 7200RPM Hybrid Internal Hard Drive (Purchased For $72.34) 
Video Card: EVGA - GeForce GTX 1080 8GB FTW Hybrid Gaming Video Card (Purchased For $509.00) 
Case: Fractal Design - Define Mini C with Window MicroATX Mid Tower Case (Purchased For $89.34) 
Power Supply: Corsair - Professional Gold 750W 80+ Gold Certified Fully-Modular ATX Power Supply 
Operating System: Microsoft - Windows 10 Home OEM 64-bit (Purchased For $0.00) 
Wireless Network Adapter: Asus - PCE-AC56 PCI-Express x1 802.11a/b/g/n/ac Wi-Fi Adapter (Purchased For $57.57) 
Case Fan: Corsair - ML120 75.0 CFM 120mm Fans (Purchased For $0.00) 
Case Fan: Corsair - ML120 75.0 CFM 120mm Fans (Purchased For $0.00) 
Case Fan: Corsair - ML120 75.0 CFM 120mm Fans (Purchased For $0.00) 
Case Fan: Corsair - ML120 75.0 CFM 120mm Fans (Purchased For $0.00) 
Other: NZXT Hue+ RGB Colour Changing Internal LED Controller (Purchased For $0.00) 
Other: NZXT USB HUB (Purchased For $26.00)
Other: NZXT GRID + (Purchased For $10.00)
Total: $1770.56
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-08-08 17:03 EDT-0400

Could be because of running auto settings on the voltage when overclocking. The motherboard may have set the voltage too high.

Cool GTX
This MB 
 
What temps were you seeing on your CPU ?
 
BIOS screen shots would help us see you setup

Temps never went past 68C under load.  I am using an NZXT Kraken x52 CLC. I did have c state 6 turned off, that's about it.  Currently, I have nothing else changed besides what is defaulted (except for UEFI / hot swap / 4.0 OC). 
 
I'll post up screen shots of the bios set up. Maybe you guys can find a fault in my settings, hopefully, I don't fry any more CPUs as I'll have to deal with Intel's return policy in 2 more weeks. -_-

Are you using a surge protector or UPS ?
 
Set Core Voltage manually --> do Not use adaptive  1.22 to 1.25 should work --> keep it under 1.4 for sure and watch your temps
 
I'd ask Corsair to test your PSU as a precaution - there was an issue with that brand previously - do not remember the specifics at this moment - however there was an unannounced change to some of the Corsair PSU
 
Found the article - link below
Intel X99 Motherboard Goes Up in Smoke For Reasons Unknown
 
(excerpt from link above:)
Update 9/18/2014 – Corsair has gotten back to us with some answers to some questions that we asked earlier this week. It turns out Corsair shipped AX760i/AX860i/AX1200i power supplies for about four months before they changed the firmware on them without notice. The firmware is not field upgradeable and Corsair will not be offering exchanges for anyone with an ‘older’ model that wants to swap out a PSU for one with the latest firmware on it. Corsair also said that by the motherboard makers [ASUS] own admission, the X99 Deluxe motherboard was the root cause for the failures.  Corsair also said this which we will directly quote: “Would an OCP-defaulted AXi or a competitor OCP-enabled PSU have save the CPU? We’re skeptical, but maybe.” So, right now it looks like the board had a failure and then when the system was restarted the PSU without OCP may or may not have taken out the CPU through the boards failed VR circuit. We are still waiting on ASUS to give us an official statement as to what happened to the board and were told that a typhoon in the region this week has slowed things down. In the meantime here are some answers to a Q&A that we gave Corsair that you can take a look at.
– When did Corsair change the firmware on the AXi series of power supplies?

AX760i/860i implementation date 3/15/2013  Lot#:13119560
AX1200i implementation date 3/8/2013 Lot# Lot#:13099520

 (AND second excerpt)
Corsair AXi Power Supply Users Should Use OC Link Software to enable OCP on their PSU if it was made before March 15th, 2013.
 
 

What's wrong with auto-voltage? 
 
Using auto-V on every board with OC CPU since CoreDuo - never single time I had any problems. On machine where I write this 5930/Classy/ is running at 4.4, loaded by BOINC to 85%, 1.309 (auto)Volts and it works like charm since I put the rig together. I never waste time with setting stuff manually.
 
Auto-1.4V at 4GHz that would be criminally bad power delivery.

Overclocking the CPU on the X99 EVGA Motherboards. Non XMP Profile BCLK Offset.
Adaptive -v- Override
 My Old Way to OC
 
  My NEW Way OC