Green led keeps flashing, no boot

Hi, my new BPI-M4 has just arrived. I connected many usb type C power adapters, using different images downloaded from : and burned and verified to a brand new SD 32GB card. But BPI-M4 keep flashing the green led and does not boot. Red led is still. There’s HDMI signal, but the screen is black. Can you please help me? Thanks in advance.