Was not aware Covid impacted the support phone line so here I am reaching out to you fine folks.
 
So some background. This computer has been built for about 3-4 years now, NO issues, AT ALL. Takes everything I throw at it but I'm also not running any crazy high settings and I'm only setup for 1080P, no 4K or anything. No crazy overclocking, did have the CPU and ram just SLIGHTLY overclocked for giggles but I dont even remember what the settings were now.
 
Build
 
EVGA 1200 Watt PSU
EVGA Z370 Classified K
I7-8700K CPU
16 GB's via 2 8GB sticks in slots 2 and 4
Western Digital Black NVMe on the bottom slot near the bottom of the board (BOOT DRIVE)
1TB Western Digital Black mechanical HDD
Corsair H150i Pro AIO
EVGA 1070 GTX SC GPU.
 
SO, on to the issue. Randomly helped someone with their computer which turned out to be driver issues and so I decided "well you know its been a while since I checked". So I download everything new straight from EVGA's Download section and install the new stuff. I notice theres a new BIOS update as of only a month ago. I think it said 3-24-2021. I'm the type that likes to get everything updated, leaving nothing behind. So I did the BIOS update. Long story short, I'm not sure what the issue even was or if it just decided "okay I'll work now". List of what I did in this order....
 
Killed power to the whole system and waited a while, tried to boot, no go, POST code A0
Disconnected the HDD, no go, POST code A0
Flipped the BIOS switch to number 2, no go, started up, hit A0 and immediately terminated the POST process, stayed off for a                       couple seconds and then tried to boot again, also hitting A0 and then hung.
Flipped it back to BIOS 1, pulled CMOS battery for a solid 10 to 12 minutes, no go, POST code A0
Pulled the NVMe and HDD, no go, and of course got POST code A2, no boot drive
Pulled RAM slot 2 and reinserted, POST code A2, so I hit F1 blind as this entire time NOTHING has woken up the monitor, POST code A6 appears. No drives present. Duh.
Tried it again with the onboard HDMI port, same result.
Put it all back together, hit the power button and it does the same song and dance, hits A0, immediately shuts off, sits for a couple seconds, and then does a NORMAL boot, NO POST CODES. Windows Update comes up and resumes its thing. 
 
So at this point, I'm obviously repeating choice words because this makes absolutely no sense. My two go to people, one that builds computers for a living and the guy I bought the GPU from, the other an IT tech. Both are just clueless and also say it makes no logical sense.
 
So I log into windows and start looking around, checking CPU temps and voltages as the Debug LED was going from 28C to 55C and anywhere between for a solid 3 minutes, then it normalized to 28C, pump at 2190 +/- 10 RPM and fans around 850-1020 RPM, normal. However, I noticed GPU is hitting 49-50C, too high for idle and doing nothing but display the desktop to TWO screen's set in the same resolution. NEITHER FAN MOVING. So I freaked, grabbed my duster blower since canned air is stupid and just blasted the GPU with air in effort to drop temps. They fall to around 35C and by that time I manually turn the fans to 100% thinking the GOLD of my PC is gonna melt (GOLD because GPU prices are like getting screwed with a broomstick right now, not the actual precious metal). Temps fall down to 30C, basically the lowest it would get at idle. Dropped fan speed to 65% and its still sitting at 30C, but I've never had to manually control fan speed before. Now I'm afraid to set it back to auto as the temp might shoot back up. I will note, that against any better judgement, I did physically touch the GPU to see if it was "hot" and it was fairly hot around whats marked on the PCB as "R731". Basically directly in the middle of the letters GTX on the lit up logo down the side of the card itself. So I believe the temp reading was correct. 
 
ALL of this happened after Intel Rapid Storage driver updates, chipset update, then firmware, system restart. In that order. 
 
Can someone help me figure out what happened and why, when my GPU is just idle, it's letting the temp get so high without turning on the GPU fans? Why would my board act bricked and then just randomly work again?
 
I've been advised to roll back by the PC builder guy but I'm legit terrified that if I try another BIOS change, its not gonna come back. I looked up the board from a reputable website, wont share to avoid breaking any rules, but they list it at over 500 dollars now so replacement is not a viable option at that pricing and all I use for motherboards is EVGA. Haven't even looked at what the next board up would be that would still take an 8700K. Point is, I want to know what happened and how to avoid it in the future and if theres any checking or diagnostic I can do from within Windows to avoid rebooting and possibly having to sit here and turn it off and on a dozen times before it will POST. 
 
As for the CPU temp fluctuations, my theory is after the pump kicked on and off 3 dozen times in the process of trying to figure out the POST issues, a bubble formed and was trapped in the pump for a couple of minutes. Its been fine since and temps are currently, at the end of writing all this, GPU 30.0C and CPU Core temps are all around...27C to 32C average @ 4% load.