Do you have a graphics card?
What input type are you using? (HDMI, Displayport, VGA, DVI)
If you are using a graphics card, is the cable going to the graphics card, or the back of the motherboard?
Most Ryzen CPU's do not have integrated graphics, so if the cable is going to the HDMI or Displayport in the motherboard, it wont display anything. I know there are a few type of AMD CPU's that have integrated graphics, but I am not so sure which ones do. I recently made the jump to AMD in my NAS at home so I do not have much experience with AMD chipsets.
Since I do not know your exact system build, based on your post you do not have a graphics card. I am willing to bet that is the issue in this case. If you want to test out the thoery, you can either grab a spare GPU from a old build maybe or even take your current graphics card out of your system if you are comfortable with doing that.