Diagnosis
The monitor is powered but not receiving a usable video signal from your PC. The input source is wrong or the cable/port is faulty.
How to Fix It
First, press the monitor's menu button. Navigate to Input Select. Change from the current setting to the port your cable uses (HDMI or DisplayPort). If that doesn't work, power everything down. Unplug and firmly reseat the video cable at both the monitor and PC ends. Restart the PC.
If That Didn't Work
The issue might be on the PC side. Test the monitor with a different source like a game console or laptop. If it works, troubleshoot your PC's graphics driver or output port.
Heads Up
Cheap or damaged HDMI cables are a common culprit. Try a different, known-good cable before assuming the monitor is faulty.