Got in my new B550 and populated it with a brand new 5700G, drives and memory and nothing, does not power up. The brick shows the green LED but absolutely no response to the power button press or hold.
Please do not use an external graphics card to boot. Try booting with the IGPU only. Or you can upload the video of the fault phenomenon to the network disk, share it with me, and I will check and assist you to solve it.