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External monitor not detected on your Mac?

A second screen that macOS refuses to see is usually the cable, the adapter or a dead port — not the Mac. Rotate through them in order and it almost always shows up.

  • Difficulty Easy
  • Estimated time 5 min
  • Platform macOS
  • Last updated
External monitor not detected on your Mac? — schematic diagram

Before you start

Low risk. This change is reversible — you can return to the previous state without professional help or data loss.

Steps

  1. Check the cable at both ends, then try a different port on the Mac — some ports are data-only
  2. If you use an adapter or dock, bypass it first: connect the monitor directly with a known-good cable to rule out the adapter
  3. Replug the monitor and wait about 10 seconds — macOS usually re-detects on reconnect
  4. Open System Settings → Displays: a detected second screen appears here as an extra display you can arrange; drag a window across to confirm it's live

How to verify the fix

The second display appears in System Settings → Displays and accepts a dragged window after you replug it.

If this didn't fix it

A known-good cable into a direct port still shows nothing — the adapter or the panel itself may be failing; on Intel Macs an NVRAM reset is the next safe step before assuming hardware death.

Next stop: the related fixes below, or start a guided diagnosis.

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