Hey! Pipeline beat me to it, and posted a picture of the inputs of your monitor.
It seems these are both inputs, but this also means you have multiple HDMI channels.
What I speculate is happening:
1 - You need to select the other HDMI Input Channel
2 - You might be using your Motherboard Outputs, make sure there isn't another HDMI port on your computer
If you haven't already checked it out, here is the user manual:
https://images-na.ssl-images-amazon.com/images/I/B1knbUmuG9S.pdf