If you've got multiple monitors hooked up to your dock and you're receiving the "No Display Detected" warning on one (or more), OR when you go to adjust your display settings, the device isn't recognizing one or more of your monitors, you may have a cable issue.
First, I'd recommend a restart of the device, just to check to make sure that all display drivers are up to date. This can also mean that when you restart, check for "updates" in the Windows search bar...sometimes you'll have "failed" ones that need to be re-tried and that can fix the display.
Next you can try unplugging the display cables from the dock then plugging them back in and restarting. Sometimes this will pick up the display.
If nothing else is bringing that display back, we need to determine if it is the monitor the cable, or the dock.
Try a different laptop on your dock. If everything works for it then the issue is the laptop (send to tech).
Try new display cables (whether they are display or HDMI) hook up new ones to the dock and the monitors, if you still get nothing, then swap out the dock. If neither of those fixes the issue then it's likely the monitors themselves.