DIAGNOSIS The monitor is powered on but isn't receiving a valid video signal from your computer. The most common culprit is the input source setting on the monitor itself or a loose cable connection.
FIX First, let's check the physical connection. Power everything off. Unplug the video cable (DisplayPort or HDMI) from both the monitor and your PC, then firmly reseat it at both ends. Make sure you're using a certified cable. Power your PC on first, then the monitor. If the blue screen persists, grab the monitor's joystick control on the back. Press it in to open the OSD menu. Navigate up or down to the 'Input Select' icon and press the joystick in. Cycle through the options (DisplayPort, HDMI 1, HDMI 2) until you see your desktop.
IF THAT DIDN'T WORK The issue might be on the PC's end. Try a different video output port on your graphics card. If you have another monitor or TV, test that cable and port to rule out a PC graphics output problem. You can also try a different type of cable (e.g., switch from HDMI to DisplayPort) if your hardware supports it.
HEADS UP If you're using a laptop dock or a KVM switch, those can sometimes cause handshake issues. Try connecting the monitor directly to your computer to bypass any intermediate devices.