When the monitor is plugged into the motherboard you will be using the intel integrated graphics.
You will need to have the display cable plugged into the GPU to be using the RX 580. Also, the GPU should be selected as "enabled" in the system BIOS.
On some displays you will need to select the input method on the monitor, such as HDMI or Display Port, depending on which method you are using.
Sometimes cable go bad so you may need to try different cables.
If you are still having problems getting a display through the GPU, you should contact Cyberpower about service or RMA options. You should not be having these problems on a new system.