Hi everyone!
A little more than a month ago I upgraded my gpu from a STRIX 1080 to a STRIX 2080TI OC, never had any issues... until a couple of days ago.
I have a 2700X, Gigabyte X470 Aorus Gaming 7 WiFi and a EVGA SuperNOVA 650 P2.
This is what happened so far:
- Yesterday my computer began freezing/powering off apparently at random after starting it and launching a game (DMC5) after a couple of minutes. After rebooting all went perfectly fine and I was able to game for a couple of hours without issues.
- Yesterday afternoon when I turned the PC on again, the same situation happened. After a few minutes, freeze (forcing a reboot). Then after reboot all ok.
- This morning, again same situation.
- this afternoon tho: every time I start an intensive game (PUBG, DMC, Tomb Raider) the issues appears after a few minutes. Sometime when it freezes, screen goes black and then the motherboard does 3 short beeps before powering off by itself, then it reboots.
 
However now even after rebooting I can't play any game. Browsing, youtubing etc works fine but as soon as I do something heavy graphic related, the issue appears. I tried Cinebench which is heavy on the CPU and nothing happened. As soon as I tried 3 mark, tho, again freeze.
 
I've found this thread here  saying it could be PSU related, but my question is: why then for a whole month I never had issues and now suddenly 650W are no more enough? I'm already using two separate cables because I knew that it's advisable with such power hungry cards but still.
 
I didn't do any hardware changes or major things... no OC, both CPU and GPU are stock clocks.
 
Any help?

powering off randomly, like you describe, is generally going to be an overheat issue.  Either the cpu or the PSU., thermally shutting down to prevent a catastrophe .
 
I would check the TIM on your cpu &/ or the tightness/ looseness of the cooler attached to it. 
 Then focus on the power supply .  How old is it ?  check those cables/ connectors as well .... and whether the fan is working correctly - how is the airflow to it  &  your case, in general .?
 
 

Could be many things. Time to test the card in another known good working system to see if the card is the culprit.

Thank you both for answering.
I don't think it's anything thermal protection related because I have good airflow, huge case (Thermaltake X5) which I also had cleaned up recently with new TIM etc...
Also I tried stressing the cpu at 100% on all cores and no freeze occured (also temperatures were ok, far from Tj max). But as soon as it's something gpu related... it's just a matter of minutes, even if temps are fine (70° C peaks max), and then everything freezes.
Most of the time it's been a freeze. Auto power off occurred only 2 or 3 times total... while the other 15 times it was a freeze. Sometimes after a freeze, when I force reboot it freezes again as soon as I login into Windows, which is also very odd considering nothing heavy is going on.
The EVGA PSU was bought new less then 6 months ago!
 
 

Yes, 650 is enough for your rig.

with your new, updated  explanation of freezing up under random times / loads..... that sounds more like memory errors.
 
Either by clocking them too high , incorrect timings, low voltage to them or even possibly going bad entirely....  but again, it is hard to troubleshoot by just listening to someone explain it.
 
I know the X470 chipsets were known for being a tad flaky with ram.

The 3 short beeps would be a memory error. I would turn the system off, switch the power off and remove all but one stick then reboot. Turn everything off and move the stick around if it doesn't boot and then try another stick until you are able to see which stick or socket on the motherboard is bad.

Hoggle
The 3 short beeps would be a memory error. I would turn the system off, switch the power off and remove all but one stick then reboot. Turn everything off and move the stick around if it doesn't boot and then try another stick until you are able to see which stick or socket on the motherboard is bad.

Yesterday night I tried removing one stick of RAM and all went fine. Started a game and after a few minutes still no freezes.

So I put the other stick back in and a started a game. Again, even after more minutes... no freezes.

I thought problem solved but this morning it's again freezing.

So nothing changed, but I'm starting to think it could actually be the ram.

I downloaded Memtest and after 5 seconds of testing my PC reboots.... so again, it might be really the ram or the slots on the mobo.

Until now I've been using slot 1 and 3 for dual channel (never used slot 2 and 4 so far so let's assume they're working), so my testing strategy will be:

- testing ram stick one on slot 2
- testing ram stick two on slot 2 

This will make sure each stick of ram works fine (at least alone) and is not damaged

- then i will test both sticks together in slot 2 and 4

If i get to this point and all goes fine then I think we can conclude either ram slot 1 or ram slot 3 has been damaged somehow.

So far MemTest showed that stick#1 works regardless of the slot it's in.... however stick#2 causes the pc to reboot a few seconds after memtest starts, again regardless of the slot it's in.
 
One of the two ram sticks seems to be faulty then. To be sure, I think I will try my ram kit in another computer (thanks to a friend who also have a Ryzen+ CPU). 


If the same stick will fail in another PC too, then we can conclude it's one of the ram stick that got somehow damaged.... do you agree?

That's 8GB or 16GB DIMM.
I think maybe even with 8GB you can try to power on system and use him some time.
Only Windows should nicely to recognize all memory and if freezing stop you know second DIMM is fault.