Mac does not detect an external display

Where this problem appears

MacBook, Mac mini and iMac systems connected through HDMI, USB-C, Thunderbolt or an adapter.

Symptoms to confirm

• The display says no signal.
• The Mac charges through a dock but shows no video.
• The display works at a low resolution or disconnects intermittently.

Likely causes

• The display is on the wrong input.
• The cable or adapter does not support the required video mode.
• A dock lacks enough power or bandwidth.
• macOS or the display firmware needs a clean reconnection.

Work in order

Step-by-step fix

1. 1

   Select the correct input on the display and confirm it works with another source if available.

2. 2

   Disconnect the dock or adapter and test the simplest direct connection the Mac supports.

3. 3

   Reconnect power to both the Mac and display, then restart the Mac.

4. 4

   Open Displays settings and use Detect Displays when available.

5. 5

   Try a known cable rated for the target resolution and refresh rate.

6. 6

   Update macOS and any dock or display firmware from official sources.

7. 7

   Check the Mac model's supported number of external displays before adding adapters.

If the main path does not work

• Lower resolution and refresh rate temporarily to test cable bandwidth.
• Test each dock port separately and disconnect other high-bandwidth devices.

How to reduce repeat failures

Use certified cables, keep dock firmware current and document a stable display configuration before adding devices.

Common questions