Zend certified PHP/Magento developer

PC wont boot and light flash when trying to power down

I have a PC i’m building with old parts from my main desktop and it wont post. It boots up and the fans spin; however it will not do anything else, even turn off. When I try to turn it off the lights in the case just flash rapidly until I flip the switch on the back.

I have replaced the PSU, Motherboard, NVMe drive, CPU, I dont know what else I can even try. (I have replaced these and re-seated them multiple times)

Specs:
CPU -> Ryzen 5 3600

PSU -> Thermaltake 500w / Corsair 650w (tried both)

RAM -> Vengeance LPX 8x2gb

Motherboard -> B450M DS3H v2 (tried the original with the updated BIOS)