Has my X-99 Pro failed or is it something else?

[Djadarian]

2 nights ago i shut down the machine, no issues. Tried to turn it on the following day and instantly something is wrong, all the fans instantly start running at 100%, the machine didn't boot into windows immediately (took a good minute or 2 longer than normal) and when it did i could see the CPU monitor said the CPU was running at 100% (it's never usually more than 20/25% on boot), i didn't know what to do so hoped once it had finished booting into windows it would just 'calm down', of course that didn't happen and a minute later i'm hit with a BSOD which tells me it's logged the error but the system will now shut down. It then restarts itself but doesn't get out of post and it tells me "CPU over temperature error!". I was planning on changing the thermal paste and giving the machine a clean anyway but it had been maybe 5 years since it was changed (during lockdown), i left the machine to cool down (as the water-cooler socket over the CPU did feel very hot). I came back around 2 hours later and just thought it'd try and start it up (the socket over the cpu had cooled). Everything started ok till it was loading up windows when it suddenly said the samsung magician software (that i have installed to monitor the M.2 drive) had failed to start (which has sporadically happened in the past although rarely), i said to close the program but the error re-appeared immediately, i again clicked to close the program, at this point (windows had still not loaded yet) it again BSOD and shut itself off. It's worth saying that the fans had kicked in above their normal level but not quite to the extreme levels they had earlier that day.

So at this point i decided this won't improve till it's cleaned. So i left it for an hour to cool down, unplugged it and started to clean (went through the 3 individual fans and the water-cooler radiator (and it's 2 fans) itself and gave them a thorough cleaning). Then to finish, cleaned up the processor (the thermal paste that was there had gone hard and very dry) and replaced that.
Fingers crossed, i reconnected all the external cables and turned it on, hoping everything would be back. The machine starts up, is very quiet now but i'm presented with a 'new CPU installed! Press f1 to enter bios'. So i thought this is strange (i had removed the cpu to clean it but was very careful with the pins and socket it sits in). I pressed F1 but was left on the 'Asus in search of incredible' bios load screen. It gave me the option to press F2 or DEL, i tried both but nothing happened. At this point i've left it running for 5 minutes expecting it to kick into bios at any time, i hear the fans are slowly getting louder again. After another minute and nothing changing (and no keyboard buttons doing anything) with the fans increasing i manually shut it off. I did a quick check and one solution people mention is re-seat the CPU again, so i did that. Restarted the machine again, this time it's quiet but it's going to post but then instantly restarting in a never ending cycle, after about 4 restarts i once again manually power it off. At this point it's almost 2am so went to bed.

Fast forward to the next morning and i go online to see what's suggested. And i found out about the Q-LED and Q-CODE that should be able to shed a light on what's happening via the motherboard itself. So i turn it on, the same process kicks in of restarting itself but it stays on long enough that the Q-CODE works through a bunch of codes before stopping on A0. I then noticed only 1 additional LED is lit up on the motherboard (outside the shut down and restart LED's) and that's above the HD which is red. Having done some additional searching this seems to be pointing to the M.2 drive being the problem (although it's only just over 2 years old). Having done a little more research i found articles saying that the bios should still kick in even without a HD, so i thought "ok, lets get into bios and sort this processor out then try and look at this HD". I remove the m.2 drive and boot up the machine. It again tells me 'new CPU installed! Press f1 to enter bios'. So i again pressed F1 but once again it hangs on the bios loading screen. And this is where i am now.

I don't have another machine i can test the M.2 in though, so i'm looking at buying an external adapter to try to connect it to my laptop and see if it's feeding anything back or if it's died. For the same reason i can't test the CPU, GPU or RAM outside of the machine they're in. I also don't have a backup M.2 to plug in and see if that resolves the red LED on the motherboard. But what's more concerning is that i've seen a few comments say "just because the error is A0 does not mean there's not a fault with the CPU, GPU or RAM either". Nothing i've seen seems to indicate that the CPU/GPU/Motherboard or RAM have failed though. When purely searching for solutions to the bios problem, a few have said to just remove the CMOS battery give it 20 minutes and put it back, that'll reset bios and if it's not working should return it to a working state, but i'd want clarification if that's worth doing or if this is all pointing to something else? Any suggestions would be much appreciated!

Apologies for the length of the message and unnecessary additions but most these threads quickly get comments with "but what happened first? we need details" type questions so wanted to cover everything.

HD: 970 Evo Plus M.2
MOBO: X99-Pro
CPU: i7-5930k
GPU: GTX 980-Ti OC Strix
RAM: 32 gig DDR4 Corsair Vengeance