Problems booting.

My original gaming PC has RTX 3060, ryzen 5700G cpu, 2x8 corsair ram, and a 400 watt power supply. These products are about 5 years old now. 4 days ago I went to turn on that pc and nothing displayed on screens and keyboard/mouse remained off while everything in computer was on, including psu fan. I researched everything. I tried switching ram out and trying different spots, I swapped HDMI cables and monitors, I tried holding power button, I tried removing the silver coin battery and even replacing it. I tried removing the gpu and using integrated graphics to boot, none of the 4 error lights displayed on motherboard, pc won’t turn off with power button. I can’t even get into BIOS. And still nothing. Most research pointed to psu being the worst part in this build. I had another 750 W psu and put that into a new pc case, bought a new mother board B550 gaming X V2 to fit the case. Put everything together and still the exact same symptoms. I even moved the ram on this new motherboard and nothing. Please let me know if anyone has any ideas. Thank you