What could be the cause of a malfunctioning LED display on a notebook computer if an external monitor displays output correctly?

A malfunctioning LED display on a notebook computer, when an external monitor displays output correctly, can often stem from a failed backlight. The backlight is essential for illuminating the display, and if it fails, the screen may appear very dim or entirely black, even though the underlying display may still be operational. Since the external monitor successfully displays output, the graphics card and driver are functioning properly, ruling out the graphics driver as the issue.

Hardware-related issues like a loose cable connection could affect display performance, but usually would cause display problems on both the notebook and external monitor. A corrupted operating system typically results in malfunctions that affect the entire system's output, not isolated to just the notebook's internal display. Therefore, a failed backlight is a likely explanation for the symptom you’re experiencing.