DIAGNOSIS The monitor isn't detecting a video signal from your PC. The most common cause is the PC's output being set to the wrong source or refresh rate.
FIX First, force the monitor to check the correct input. Use the monitor's OSD button to manually select 'HDMI 1' or 'HDMI 2' (whichever port you're using). If that works, your PC's auto-detect failed. If it doesn't, reboot your PC with the monitor on and connected—this often forces the graphics driver to re-handshake. Finally, check your Windows/NVIDIA/AMD display settings to ensure the output is set to 1920x1080 and the refresh rate is 60Hz or 144Hz/160Hz, not an unsupported mode.
IF THAT DIDN'T WORK The included HDMI cable can be low quality. Swap it for a known-good, high-speed HDMI cable. Also, try a different HDMI port on your graphics card to rule out a dead port.
HEADS UP If you're using a GPU with both HDMI and DisplayPort, the PC might be defaulting to the wrong one. You need to set the correct output as your primary display in your graphics control panel.