Question Computer screens go black, devices disconnect, pc stays on but cannot be turned off unless using psu switch

[Eletrix]

In the past week my computer has been doing this thing where my monitors go black and get no signal then all of my usb devices connect will show no sign of being powered but my pc says that it is on and the fans are spinning usually happens from 5 minutes to 1 hour of usage. When it does this i can’t turn it off using the power button no matter how long i hold it so i have to use the PSU manual switch. Sometimes the pc will even just turn off instead out of no where. This is not a temperature problem as I have monitored temps and reapplied thermal paste several times. I have reassembled the pc and it seems to have not fixed anything. I have also gotten a new PSU so that cannot be the issue
Specs:
CPU: Ryzen 5 3600
GPU: Geforce RTX 3060ti Founders Edition
RAM: 32gb OLOy 4x8 ddr4 3000mhz
PSU: Phanteks (PH-P650G_US01) AMP Series 650W 80PLUS Gold
Motherboard: Gigabyte b450m ds3h
please help me.

 

[Theskywillraindeath]

All those separate issues would lead me to believe it's a faulty motherboard. I would try replacing it with a B550 mobo. since those are cheap as chips these days.