Pc will only turn on if I hold the button

When my pc is off, if I press the power button it just briefly flashes and turns off. If I hold it the power button it flashes, turns off, then turns on and it’s fine. And when I try to wake it from sleep it flashes and shuts down completely. A little while ago the motherboard died for no apparent reason and this problem only happened after I replaced it. I’m thinking it may be the PSU?

Specs: RTX 3070 Ryzen 5600x T-force delta rgb 16gb x4 MSI B550 gaming strix Thermaltake 750 watt smart RGB PSU