Check your hardware and ensure the HDMI port on your computer is working correctly.
Check the quality of the cable you are using and ensure it has the ability to transmit 4K vision.
If computer doesn't have an HDMI port check the HDMI adapter is in good condition and is successfully working on another device. Restart your computer and reconnect your HDMI cable.
Ensure the device you are outputting to can handle 4K images. If it is unable to handle 4K go to Inputs and select the icon in the bottom right of the window.
Scroll across to 'menu settings' and change 'HDMI out' to 1920x1080 which will lower the screen resolution of the panel.
If none of the solutions above fix your problem then please raise a support ticket :)