The correct answer is 'Check the monitor's backlight or inverter'. When a monitor's image is dim despite proper brightness settings, it often indicates a problem with the backlight or inverter, which are responsible for providing the necessary light to the screen. Without functioning backlight or inverter components, the image appears dim regardless of the configured brightness level. Other options, such as adjusting the contrast or checking for eco/power-saving modes, are unlikely to solve the problem when the brightness setting has already been confirmed to be at the appropriate level and the image is still dim. Checking the video card does not immediately relate to the brightness of the monitor's display.