DIAGNOSIS The monitor is not detecting a valid video signal from your graphics card. This is usually a cable, GPU setting, or power setting issue.
FIX Replace your video cable. This is the most common fix. For 4K 60Hz, use a high-speed HDMI 2.0 cable or a certified USB-C cable. If using USB-C, ensure your GPU/USB-C port supports DisplayPort Alt Mode.
IF THAT DIDN'T WORK Disable power saving on the monitor. Press the joystick. Go to Menu > Display > Power > Power Savings. Set it to Off. Also, check your computer's power settings. In Windows, set 'Turn off the display' and 'Put the computer to sleep' to Never.
HEADS UP If you use an adapter (like HDMI to USB-C), it may not support the monitor's required EDID data. Use a direct cable connection. A faulty cable can also damage the monitor's input port.