Question z97-k: CRASH, tthen need to reset CMOS to even get into BIOS. help?

[sz0ty0l4]

So this started like 3 week ago. for 2 days it happened continously.. i booted up, surfed the net, played games, then PC started suddenly crashing: black screen, restart, no boot , cant get into bios. What i did: reset CMOS, then flashed BIOS to latest version from asus site.
For 2 weeks i played my games and so on without any problems.

Today: it started again. while browsing google, PC suddenly restarted, and same issue as described above...
components:
z97-k
i7 4790k, 4.4ghz 1.26v, tried stock setting ofc, it seems that the issue isnt related to how the CPU is set. it crashes on default settings aswell.
gtx 1080ti
16gb ram
FSP 750 hydro G

what i have checked already:
Temps are fine( 65-75 generally based on Load), 75-80 in stress tests
if i run stress tests like prime 95, there arent any errors whatsoever.
I ran memory diagnostics, it says my RAM modules are OK.
PSU voltage regulation seems OK( checked during stress test)

I dont know what to think. I admit. the CPU and MOBO are in fact OLD. both like 4-5 years.
Is this the end of either of them? Is there anything i could do, or just look for a new config?

 

[Metal Messiah.]

A system restart/reboot points out that the PSU might be the culprit, imo. Not sure though. But since you have already tested the PSU, I assume it should be fine ? How old is your power supply unit, by the way ?

EDIT: BTW, does the system reboot even when are using the motherboard's Integrated Graphics Processor, instead of the GPU ?

 

[sz0ty0l4]

Well i’m not sure. I think if it would be the PSU the system would have not been running for 2 weeks without issues running hours of prime95 and rog realbench on full load. It isnt a restart and not a reboot either. Its like a total system failure. Pc powers down then powers up but cannot boot or go into bios. Need to manually reset cmos battery and then set bios to default to even boot. I was thinking maybe it could ne a contact error or a short somewhere ? I dont know what to check :/