How to Fix Help needed! Lost external displays During macOS Boot or Installation

Apps Boot guide iMac MacBookPro macOSMonterey OpenCore OpenCoreLegacyPatcher Performance
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How to Fix Help needed! Lost external displays During macOS Boot or Installation

Boot failures need a predictable pass through firmware, USB, storage, EFI and verbose logs before reinstalling macOS. Most installer stalls come from firmware settings, an invalid config.plist, wrong SSDTs, bad USB mapping or unsupported storage/controller settings.

Quick Checks

  • Backup current state: Save a copy of your working EFI and run a full system backup before changing settings.
  • Identify hardware components: Note down your exact CPU, GPU, Wi-Fi card, and motherboard/laptop model.
  • Ensure utility alignment: Keep OpenCore, OCLP, and ProperTree updated.

Fix Steps

  1. Create a rollback point: Make a Time Machine backup and keep a copy of your last working EFI folder before editing OpenCore, kexts or root patches.
  2. Boot verbose: Add -v keepsyms=1 debug=0x100 so the final visible line gives a real clue.
  3. Check firmware settings: Disable Secure Boot and Fast Boot, set SATA to AHCI, disable CFG Lock if possible, and use UEFI mode.
  4. Validate OpenCore: Update OpenCore, Lilu and core kexts, then run ocvalidate or ProperTree clean snapshot.
  5. Recreate the installer: Use a fresh USB installer and try another USB port; older Macs may need a USB 2.0 hub for input during setup.
  6. Reset NVRAM: Reset NVRAM from the OpenCore picker before retrying the installer.

Do Not Continue If

  • Do not continue if: you do not have a working EFI backup, a Time Machine backup, or another bootable macOS installer.
  • Stop and capture evidence: if the machine stops booting, take a photo of the last verbose line before changing more settings.

Verify It Worked

  • Verbose boot moves past the previous stopping line.
  • The installer reaches Disk Utility and sees the target disk.
  • Keyboard, mouse and USB remain active during recovery.
  • OpenCore picker still loads after a cold boot.

Rollback

  • Restore the last booting EFI folder.
  • Use the officially supported macOS installer to recover the machine.
  • Do not erase the internal disk until the installer can boot twice consistently.

Next Action

  • Test now: reboot twice, reproduce the original problem, and confirm whether the same symptom returns.
  • If it still fails: record the Mac model, macOS build, OpenCore or OCLP version, GPU, Wi-Fi/Bluetooth chipset, and the last visible error.
  • Read next: use the related searches below for the nearest OpenCore or OCLP fix before making another change.

Related iATKOS Searches

Original Question: "Help needed! Lost external displays"

Hello, i really need some help. I have a Late 2015 27inch iMac running Monterey 12.7.4. I am an absolute novice to most computer things and definitely OpenCore but being stubborn I have been trying to find a way to use this iMac as a monitor for my MacBook Pro. I found this YouTube link https://www.youtube.com/watch?v=sO0yc3_hOE8 and thought fantastic! I'll try it. So I used the latest patch showing in the link provided in the video and followed the videos instructions of creating the boot drive and running the program by choosing to boot to that drive and YAY! it worked. There was airplay and I could connect to it. I didn't have a lot of time, so I just put my laptop away and went back to using my 2015 iMac with two external displays as I always have — I did not boot out of OpenCore—and 24 hours later in mid-use <poof> no more external displays. I cannot get the iMac to recoginize the two external displays that I have been running on this system for the last 5 years. The opencore patcher must have changed something. I tried rebooting without the OpenCore patcher boot disk, as the video stated that would put my Mac back the way that it was before ever using OpenCore but nope. Airplay is now not showing but still no external displays. Pushing the option key in the display settings does not make Night Shift switch to Detect Displays so something is clearly wrong. I am panicking. I use this mac for work every day. I have zero idea how to troubleshoot this or what to do. Of course I did not make a Time Machine backup. Can I get it back to how it was before OpenCore? Can anyone help me figure out how to troubleshoot this and hopefully walk me through getting my displays back? I wont be able to really work on this until tomorrow though, I am in the US Eastern time zone. I really really really would appreciate any help. I am so lost.

submitted by /u/KathCobb
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