If your computer doesn’t recognize an external monitor, it’s often due to connection problems, compatibility issues, or outdated drivers. First, check that the monitor is properly connected to the computer and power source. Switch to a different port on your computer or try a new cable to rule out faulty connections. If you’re using an adapter, ensure it’s compatible with both the computer and monitor. Next, go to the display settings and try detecting the monitor manually; on Windows, there’s usually a 'Detect' button. Sometimes, an outdated graphics driver prevents the computer from recognizing additional displays. Updating or reinstalling the graphics driver via Device Manager can help resolve this. For ongoing issues, connecting the monitor to a different device will help confirm if the problem is with the monitor or computer.