Question Pc turns off randomly and would shutdown again after few minutes or hours

Dec 19, 2019
My System Specs:
i5 6400
16gb ddr4 2166 mhz single stick
Gigabyte h110 m-h Motherboard
Thermaltake 600w Psu ( Before)
Seasonic 500w (Now)

So i got this system with thermaltake 600w psu and it would turn off randomly and then it wont even pass windows logo and would keep restarting and kept following that cycle.
I replaced Pus with seasonic 500w and New dell case. System worked fine for few days but again it would start shutting down randomly and would restart but again it would shutdown at some points after few minutes. on any windows application and even when it is idling in bios. I have to unplug Ac power switch and then I would get few more minutes of uptime and sometimes it would never shutdown for 3-4 days.
I have tried different psu and different HDD and SSD but the problem is still there. There is no sign of overheating cpu is around 60c max temp .No sign of damage on motherboard but when pc turns off North/South chipset with heatsink appears to be hotter than other parts of motherboard but that too feels like 60c ( Because my gpu feels hotter and I have same problem without gpu).

What could be the issue as I have tried 3 different PSU. No sign of heating .I am thinking it might be motherboard issue but I am not sure about.

I have read old threads and mostly people solved it using different psu or sometime it would go away randomly.

When it shutdowns ,there is no sign of screen glitching or freezing or beep sound just instant powercut.