My new MacBook Pro suddenly stopped recognizing external monitor (Dell U2515H) after 2 days of normal usage.

Yesterday, after I was done with my work, I closed the lid as usual and today, I opened the MacBook and the external monitor didn't get detected.

The monitor is connected via USB-C -> HDMI cable (cost about 20$).

I have already tried restarting my mac, reconnecting the monitor and detect monitors in system preferences. I have also tried reseting SMC and NVRAM. Unfortunately none of it worked.

Detailed info:

  • MacBook Pro (2018) - 15", i7
  • Mac OS High Sierra - 10.13.6
  • USB-C to HDMI cable
  • Monitor: Dell U2515H

Any help is highly appreciated as I really need my external monitor for work.

  • I think the most productive thing to try would be to connect the adapter and display to another MacBook Pro of the same type to see if the replacement MacBook Pro works. Also, when you performed the NVRAM reset, was anything other than the power supply connected? If you're not sure, try it again with nothing other than the power supply connected. – Trellis Aug 3 '18 at 1:24
  • @Trellis Thank you for your reply. Reseting the NVRAM with nothing connected didn't help. The problem is that I don't have another MBP and I don't know anyone with same MBP. – Phyber Aug 3 '18 at 6:54
  • The only really reliable way to identify a problem with a hardware configuration is to isolate devices and replace each one. That's much more difficult, of course, when you're the only person you know with the same hardware configuration. Apple store might be able to help, because they can duplicate your Apple products (computer and adapter), or come close. The first step I would take in your situation would be to be sure the display works with any other computer. If it does, you might then consider taking all three components to an Apple Store Genius. – Trellis Aug 3 '18 at 22:55
  • There's a chance that you can find something in logs, but it's different comparing log history since Sierra. You might find a way to use Consolation3 to dig through old logs to compare what happened when you used to connect the display successfully with what happens now, but I wouldn't know how to go about it offhand. – Trellis Aug 3 '18 at 22:55
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    @MdaG Unfortunately not. Still trying to find a solution to this. I have ordered new cables to try, however none of them came and my order has been cancelled. Maybe try starting a new question, hopefully someone who can help notices it. – Phyber Aug 30 '18 at 17:35

This might seem silly but this worked for me (also better to exhaust all options):

I use a dock connected into the thunderbolt port. My charger connects into the dock and so does the monitor (dp to mdp cable). My Dell U2715H suddenly stopped working too. I tried a bunch of different things but nothing worked. I decided to take my laptop to a service center. I just happened to remove my charger from the dock first (with the monitor still connected) and suddenly the desktop showed up on my monitor and every thing was working fine. I just connected my charger back and everything was back to normal.

  • Amazing! I spent so long trying so many different things and this fixed it for me. Thank you. – duffn Dec 18 '19 at 14:54

I had the same issue with Macbook Pro w/touchbar, but with 2x Dell u2415Q (both stopped working at the same time). They are connected via 2x Kanex USB-C to DisplayPort female dongles; then using standard DisplayPort cables from there.

After much faffing around, the solution ended up being to simply disconnect the dongles, from the cables, and reconnecting at the dongle level. I had tried disconnect from Macbook, and disconnecting from the screens, but didn't try disconnecting the middle connection (separating the dongles from the cables and back again).

All up and running again. Hope it helps someone!


I had same problem. Spent an hour with Apple tech support, we finally figured out I needed a USB-C to miniDisplay port dongle, not the USB-C to Thunderbolt 2 dongle I purchased with the new MacBook Pro. (Outward appearance of the miniDisplay port and the Thunderbolt 2 port are the same.) Once I had the right dongle, the monitor worked immediately.


Had a similar problem MacBook Pro 2018, Belkin dock and USB-C HP monitor.

  • go to System Preferences > Software Updates
  • install all pending updates
  • reboot

Now it is working again.

  • What exactly do you mean by "all updates"? All updates to what? Also, did the updates include a reboot of devices? – nohillside Jul 29 '19 at 8:45
  • Welcome to Ask Different and thank you for your answer. :) Unfortunately, short answers such as this don't really provide enough detail or context to help many users. If possible, it'd be good if you could add some more info such as what updates you installed? Also, you may want to read How to Answer for tips on providing answers here. – Monomeeth Jul 29 '19 at 9:10

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