Forgiveness. The error description is a bit confused. Which HDMI ports do you speak of? As far as I understood / guessed only Port1 works on the screen.
Set the screen to the delivery state. Then turn off the screen and PC and disconnect the power plug. Also remove the HDMI cable. After 5 minutes, just turn on the screen. Convince yourself of the delivery state.
If so, you can connect the PC to the screen on Port2. Pay attention to the correct quality of the cables.
Start the PC. Please report the result.