Why is my second monitor not detected on my Mac?

This problem can be very annoying. Here’s a detailed approach to tackle it:

1. Recheck Connections: Verify that all connections, including power, are tightly secured.
2. Terminal Commands: If you’re comfortable in the Terminal, use commands like sudo killall -HUP coreaudiod to reset system services.
3. Safe Mode: Restart your Mac in Safe Mode by holding Shift to see if the monitor is detected, which can bypass software issues.
4. Arrange Displays: Go to System Preferences > Displays > Arrangement tab and drag the display icons to match the physical monitor setup.
5. Quality Adapters: Avoid generic adapters and opt for reputable brands or Apple-certified ones, which can resolve connectivity problems. Switching from a third-party adapter to an Apple-certified one fixed the issue for me.

First, confirm that both your Mac and the monitor are turned on and connected correctly. Here’s a step-by-step guide that helped me solve a similar issue:

1. Check Connections: Disconnect and reconnect all cables firmly. A loose connection can often be the root cause.
2. Detect Displays in Preferences: Navigate to Apple menu > System Preferences > Displays and click on ‘Detect Displays.’
3. Try Different Ports: Use different ports on your Mac; sometimes specific ports or cables might have issues.
4. Update macOS: Ensure your macOS version is up to date as updates can fix peripheral bugs.
5. Restart Your Mac: Simply restarting might refresh the system to recognize the monitor.
6. Reset NVRAM/PRAM: Shut down and restart your Mac holding Option + Command + P + R keys to reset certain system preferences, potentially resolving detection issues.

Following these steps should help you resolve the issue.

I contacted Apple Support and here’s their advice:

1. Software Updates: Go to System Preferences > Software Update and install any available updates. Updates can often fix peripheral detection issues.
2. Screen Saver Off: Ensure that screen savers are turned off as they can conflict with multiple displays setup.
3. PRAM/NVRAM Reset: To reset PRAM/NVRAM, restart your Mac while holding Command + Option + P + R until the second startup sound. This action resets system preferences that might resolve display issues.

These steps recommended by Apple Support resolved the issue for me.

Here’s a simplified checklist that worked for me:

• New User Account: Create a new user account on your Mac and check if the monitor works under it. This can pinpoint if the issue is specific to your user profile.
• Correct Input Source: Double-check that the monitor input source (e.g., HDMI, DisplayPort) is correctly set on the monitor.

I faced the same problem last week and here’s what I found worked:

• Double-Check Display Settings: Ensure that the displays are set up to mirror or extend properly in the System Preferences.
• Cable Compatibility: Switch out cables as some may not be fully compatible and try different combinations to support your monitor’s resolution and refresh rate.
• System Report Insight: Head to Apple menu > About This Mac > Overview > System Report and see if the monitor appears under Graphics/Displays. If it’s listed, the issue is likely software-related.
• SMC Reset: Perform an SMC reset by shutting down your Mac, then pressing Shift + Control + Option on the left side along with the power button for 10 seconds.

These steps resolved my issue and I hope they will do the same for you!

If your monitor isn’t being detected, checking the resolution and refresh rate settings might resolve it:

• Ensure that the monitor supports the settings configured on your Mac.
• Try lowering the resolution and refresh rate in System Preferences to see if the monitor gets detected. This simple adjustment made a big difference in my case.