MacBook won't detect external display

Brand new 2017 macbook pro 13 inch w/o touchbar. Two brand new genuine Apple USB-C/Thunderbolt 3 to Thunderbolt 2 / mini-displayport adapters. Tried NVRAM reset, SMC reset, DisplayLink drivers, etc. Nothing makes it work. Tried two DVI monitors via a mini-displayport to DVI cable and two Apple Cinema Displays (all working on other laptops) and none work on this brand new macbook. The dongles and monitors both work fine on another late 2016 15 inch MBP.

I just tried to hook my iMac (27 inch late 13) running 10.13.3 as a second screen to my MBP(retina early 13) also running 10.13.3 and no luck. I have been using the iMac as a second screen for the past 2 years at work and now it just does not connect. Does not find it at all. HS has so many glitches that it's not even funny. Tried a different monitor HP and nothing.... High Sierra is doing my head in.... anyone has any leads??? Reading so many different threads but nothing have worked so far 😟 HELP!!!

I had the same problem, the macbook pro 2017 would not recognize the HDMI 27" monitor (brand new & high res) when connecting it through a number of converters or a multiport C connected hub with an HDMI output. I decided to simplify and bought a USC-C to HDMI converter cable from DDUP on Amazon for $20.

(DDup USB C to HDMI Cable 4K 60Hz, USB 3.1 Type-C to HDMI Cable for Macbook/Macbook Pro/ iMac, Samsung Galaxy S8/S8+/Note 8, ChromeBook Pixel/Pixelbook, Surface Book 2, LG V30, Thunderbolt3 - 6 Feet).

I plugged it in on the right had side c port (where the mini DVI display port was in past generations) and it popped right up - auto recognizing it.

Also - if you want a terrific, affordable 27 inch monitor for your new macbook pro, I highly recommend the

ASUS 27" WQHD (2560 X 1440) IPS DP HDMI VGA Eye Care Monitor 27-Inch Screen LED-lit Monitor (VZ27AQ) from Amazon for $320.

It looks as sharp and clear as the Mac's retina display, very impressive, at a reasonable price.

This is annoying. I teach and jump from classroom to classroom with my mid-2012 MacBook Pro and connect to various TV's and projectors. Since updating to High Sierra, I can only do video mirroring. When I try to use our awesome Ultra 4K television as a second monitor, my MacBook Pro screen goes black. Only one time out of one hundred when I reset the PRAM or SMC will it work- except that in that rare case I lose the ability to control monitor settings from the menu bar and have to keep opening system preferences. However, for the last three weeks, nothing I do will bring back my ability to use external projectors and monitors as a second monitor. I called Apple a couple of times and they were no help. This is an important issue and I wish they would address it! AND- this advice to buy an new monitor is not good advice. This is a software issue.

just wanted to post this here in case someone had same issue as me. MacBook Pro, High Sierra OS. I use a Thunderbolt to HDMI cable to view my screen on my SAMSUNG TV. Did you know the Thunderbolt cable can plug into my MacBook right side up and upside down? And guess what - only one way allows the monitor to be recognized/detected. I never knew a cable - which can be plugged in either way - would not work either way. Lesson learned.

I installed High Sierra on my Macbook Pro and then my mini display-port to HDMI stopped working. I tried every reset and different HDMI cables, nothing worked. Then I found the problem. When installing major updates on Mac's if you leave devices plugged in, as the computer restarts several times during install power surges through your ports can knock out your external devices. Well that's what happen, it broke my mini displayport adapter. after using a new one, problem solved. High Sierra or Sierra can knockout Thunderbolt docks, display adapters or anything connected to your computer. So next time, unplug everything connected to your Mac before updating.

I'm almost positive this cannot be accurate. You may have had a short or a dongle that High Sierra doesn't support and it seemed like High Sierra knocked out your ports. My adapter works as it always did on an older HDMI TV but only works SOMETIMES with my new TV when it used to work in mirror or second monitor mode ALL the time before the update. This is a software issue.

What I'm saying is, when all else fails and you've tried everything recommended, then replace adapter or cable that you use. I had a friend with an extra adapter and didn't have to buy one. But of course, this can only be the problem if your external devices were connected during upgrade, if not connected at the time then maybe a software issue is the problem. I'm don't needing to try anything else because replacing my adapter worked. Someone suggested that my adapter went bad on it's own and I've seen that happen before but at the exact time of update, I don't think so. The High Sierra security update is to prevent a flaw in the Intel chip set that allows someone to meltdown your chip set or burn up your battery so maybe this update can surge power settings through your connected devices. It best to disconnect everything before upgrading and then you know for sure the upgrade cannot damage your external devices. There's to many people posting trying all other solutions and nothing helping. This is just one more suggestion, when all else doesn't work. It worked for me. It's harder for people with Thunderbolt hub's because they cost so much.

That worked one time for me. It usually doesn’t though. With one particular projector connection, I have to restart my computer just to get my computer to recognize the connection. All these problems didn’t exist until upgrading to High Sierra.

Agreed - currently struggling to see why I should stick with OSX; poor backward compatibility, insane hardware decisions (flagship laptop has irritatingly clicky zero-throw keyboard, can't plug in anything without a dongle, unimpressive battery life, pointlessly huge trackpad with unresponsive 'simulated' button clicks, replaced function keys with Touchbar you have to look at every time you want to press a key like ESC| etc.), and now failure to reliably perform something as basic as plugging in an external monitor! Oh, and the manufacturer saying it's our hardware at fault when it all worked with the previous OS release. Works about one time in ten: Not sure this is something I can rely upon as a professional.

I've been having the same issue with both my iMac and my Mac Book pro. They no longer connect to a monitor that I have been using for years, but my fiance's windows computer can, so I know it's not the monitor or the cord. I use a lightening adaptor to whatever the standard monitor cord is with the pokey pins (as you can tell I'm really techy). My monitor is a hella old (technical term) Dell monitor.

I tried all the suggestions including downloading the display link driver and that didn't work. Tried resetting SMC (while disconnected from the monitor) and that didn't work.

HOWEVER, user Pooh1952's suggestion did work (thanks!):

With the monitor plugged in, I turned the computer off, then back on and reset NVRAM & PRAM by holding cmd/opt/p/r when I heard the startup sound until I heard it again. Logged in and the display worked!

BUT, when I unplug the display and plug it back in, it stops working. I only need it for my iMac though so I should be able to just keep it plugged in. It stays connected when it's asleep but I haven't tried restarting it yet... <:\

Best of luck everyone! This is stupid. 😀

Yeah this blows. I finally got the adapter so I could connect my 2017, 15” MacBook Pro to my 27” Apple Display ... worked for one day and then I upgraded to High Sierra—nothing. Just the idea that an Apple rep suggested we’d have to sell our monitors and take a stab in the dark at getting a new one is ridiculous and unacceptable. Maybe Apple should buy the monitors back from us since they rendered them useless. Especially the actual Apple monitors. I smell a class action suit if they don’t address it. Jobs is rolling in his grave.

That's what we had to do! I work for a school district and our IT dummied down our OS then we installed some of our software. Then upgraded and now it works.The things that didn't work We dummied down the computer To OS previous and left them. Now we're looking for a touch monitor that will work with them. Getting ready to ask the question now!

I am having similar issue using an HDMI 3X1 switch that was working initially. The switch is working with my Windows 7, but not with my 2017 MacBook Pro. If anyone has any solution, I am open for suggestions.

Okay. Full disclosure (even though I tried this a couple times before) it seems unplugging the monitor—at the source (not just from the back of the monitor) for 15+ secs and then plugging back in cleared up the issue. 😐

My 2017, 15” MacBook Pro is now connected via third-party mini display port to usb-c adapter, to my 27” Apple Display and working perfectly as I type this. Crisis averted, for me anyway. Good luck everybody.