I recently ran into a frustrating problem while trying to connect my MacBook to an external Samsung monitor using an HDMI cable. When I plugged it in, a prompt appeared asking me to "Allow Accessory to Connect," but before I could click anything, the prompt disappeared in just five seconds! Now, my Mac thinks the connection is a security threat and has permanently blocked the HDMI output. I've tried unplugging and replugging the cable, restarting my Mac, and adjusting Privacy & Security settings, but nothing seems to work. My husband, who works in tech, also spent 40 minutes trying to solve it without success. I'm really struggling to get my second screen back so I can finish my work. Has anyone else experienced this issue, and do you know how to make the Mac forget the blocked connection?
4 Answers
That’s pretty unusual! I've never encountered such a strict timeout with an HDMI device. Google suggests checking System Settings, then Privacy & Security to adjust "Allow accessories to connect" settings. You might find an option in there to change how it behaves.
It could be a USB-C to HDMI adapter issue, where it's recognized as a hub. Just a thought!
My husband finally managed to fix it after some digging! He went into the hidden Library folders and deleted the display preference caches. The timeout caused macOS to permanently block the monitor in those hidden files, but after deleting them and restarting the display engine, everything connected perfectly again! I'm so relieved; I can finally focus on my work!
Glad to hear you got it sorted! That 5-second window can be a nightmare.
To resolve this issue, you can edit or remove the display preference files on your Mac. There are typically two files: one in your Home/Library and another in the System/Library preferences folder. That should fix the timeout problem you experienced.
If you're still having trouble, try unplugging the monitor from the wall and pressing its power button for five seconds. Then plug it back in and connect to your Mac again.
I actually tried that, but it didn't work for me.
Thanks! My husband fixed it by clearing the cache since the Mac blocked the monitor, so all is well now!