My Mac can't see my monitor
August 25, 2018 9:36 AM   Subscribe

I have a very new MacBook Pro OS with High Sierra. I've been using it hooked up to an external monitor. I took it to work because of problems using Word. The IT guy fixed it, but now it won't hook up to the monitor. I took it back in, and he was able to hook it up to an external monitor there, but it still doesn't work at home. He doesn't think anything he did would affect the way it works with the monitor. Help!

I really, really need to be able to use the external monitor in order to use my Mac in any meaningful way, so this is a huge problem. Also, I don't know anything about computers, so if you can help me with this, assume you need to explain anything you tell me to do. Online instructions usually assume I know things I don't.

The problem seems to be that the Mac doesn't know it's connected to the monitor. When I go to Display and try to use mirroring, it doesn't show another monitor (it did at work - that's how I know what it's supposed to look like). I have the box checked that says to show mirroring options in the menu bar, but it doesn't. Per our IT guy, I've tried unplugging and replugging everything multiple times. I've checked all the connections on the monitor. I've tried restarting. I've tried using a different dongle.

The monitor is really huge, so it's not something I can easily take somewhere to have someone try to figure it out. It was working perfectly before, so it's not something that's impossible with my Mac. I don't really know anyone I can ask to come over, but I would be happy to throw money at this if that would help.

Thank you!
posted by FencingGal to Computers & Internet (21 answers total)
One more thing I should add: the monitor says "No DP signal from your device."
posted by FencingGal at 9:38 AM on August 25, 2018

Also seeing a thing that says "USB Accessories Disabled. Unplug the accessories using too much power to re-enable USB devices."
All of the directions I see for resolving this involve pressing the power button. Please tell me if there's a power button because I don't see one. It turns on when I open the lid.
posted by FencingGal at 9:43 AM on August 25, 2018

I am not sure about your monitor issue but the on/off switch for the newer Pros is on the right side of the touchbar. You can see it in the image if you scroll down on this page.
posted by jessamyn at 9:46 AM on August 25, 2018

You haven’t said what kind of monitor you have, but you should check if there is a button on the monitor to switch between the inputs. The message the monitor is showing you is basically saying “nothing’s plugged into my DisplayPort hole” and if you’re using a different connection (like maybe HDMI) you just have to tell the monitor to use that one instead.

You should also make sure the cable is connected to an input on the monitor and not an output. For instance, if you have a Dell monitor like this one, number 3 is an input and number 5 is an output for daisy-chaining to another monitor.
posted by bcwinters at 10:13 AM on August 25, 2018 [2 favorites]

This is the monitor.

I haven’t changed where any of the cables on the monitor are plugged in, and it was working perfectly before.
posted by FencingGal at 10:21 AM on August 25, 2018

Do you have the MacBook open on closed when you connect? Is the Mac connected to power? The default behavior is to sleep when closed if no power is connected. The Mac should "blink" it's own screen when it thinks their is a new monitor to configure. What sort of cables / adapters are you using to connect the port?
posted by nickggully at 10:26 AM on August 25, 2018

These big dells happen to have multiple inputs, and may not "switch" to the active plug. Try in the on screen menu switching "active" ports, then unplug/plug the monitor.
posted by nickggully at 10:31 AM on August 25, 2018

Mac is open and connected to power.
I’m using this cable.
I don’t know what onscreen menu you’re referring to or how to get to it.
posted by FencingGal at 10:48 AM on August 25, 2018

On the side of the monitor should be four-ish buttons, may be concealed under the lip on one edge. You will hit a menu option, and then there are up/down select. Usually adjacent to a power button.
It is an awkward interface, but you should be able to get to "inputs", and cycle through those to figure out which one is wired to to the computer.
posted by nickggully at 10:53 AM on August 25, 2018

I found Input Source. It has DP checked. I moved it so that bar was also highlighted, unplugged the monitor and plugged it back in. Still getting same message that there’s no DP signal.
posted by FencingGal at 11:04 AM on August 25, 2018

Can you make sure the cable is firmly plugged into the input (not output) display port on the underside of the monitor? Can you switch USB-C ports on the Mac? (The back right one is slightly different than the others).

Does the MacBook Pro have "GPU switching" enabled? It should be on to power this big display.
posted by nickggully at 11:11 AM on August 25, 2018

I’ve checked all the cables multiple times.

I can’t figure out if I have GPU switching enabled. Google isn’t helping me there.
posted by FencingGal at 11:22 AM on August 25, 2018

If it matters, the Bluetooth connection to my keyboard isn’t working either. I hit connect and it says it’s not connected.
posted by FencingGal at 11:31 AM on August 25, 2018

The USB error points towards the MacBook being unhappy and perhaps not wanting to pair with other devices. You might try an SMC reset and see if it starts pairing with things again.
posted by nickggully at 11:39 AM on August 25, 2018

That didn’t help. Now the keyboard doesn’t show up at all. Thanks for trying.
posted by FencingGal at 11:54 AM on August 25, 2018

It sounds like the USB bus (which runs basically every peripheral, including the internal keyboard, mouse, and Bluetooth) may be borked. Since you have an almost new computer( meaning you probably have AppleCare) a visit to an Apple Genius Bar or other Apple certified repair shop, is in order.
posted by rockindata at 12:31 PM on August 25, 2018

I would definitely try taking it in to the Genius Bar, if possible, especially since you're experiencing trouble with the keyboard.

However, I encountered a similar problem with connecting a new Mac Mini (running High Sierra) to a new external HP monitor , too. I was trying to use the Thunderbolt to HDMI connector. I learned the hard way, after trawling the Apple Support boards that, for whatever reason, that combination doesn't usually work with High Sierra. I tried all the recommended resets and fixes to no avail.

I ended up switching to a VGA adapter instead; works fine now. Upshot, you might try a VGA cable if you have one handy to see if that works.
posted by skye.dancer at 5:22 PM on August 25, 2018 [1 favorite]

A longshot theory: you were using a DisplayLink adapter and the IT guy updated you to 10.13.4 or higher, which breaks this: See
This could also explain your USB messages since that's how DisplayLink connects.
posted by soylent00FF00 at 6:33 PM on August 25, 2018 [1 favorite]

USB-C is still a bit wonky.

Most USB-C cables have a bunch of chips in them - active cables.

The cable you posted is a 4k-60 USB-C to Displayport cable, and that's an active cable.

Make sure you remove power from both sides of the cable by unplugging it from both the computer and the monitor.
posted by tomierna at 7:07 PM on August 25, 2018

Skyedancer, would that be a possibility even if it was working with this monitor and keyboard for months? I had no problem at all until I took it into the office. Now the Bluetooth doesn’t even register that the keyboard exists.

I will take it to the Genius Bar. Thanks to everyone.
posted by FencingGal at 7:37 PM on August 25, 2018

FencingGal, the fact that the monitor used to work with the Mac and your new problem with the keyboard makes me suspect--like rockindata--that there might be something else wrong, such as a problem with the USB bus. My idea is a long shot that could be used to potentially diagnose the source of the problem. For instance, if a switch in cable does work, that could give you more information about what is wrong and make it clear that the keyboard/Bluetooth problem is separate from the monitor problem.
posted by skye.dancer at 12:25 PM on August 26, 2018

« Older gifting minefield   |   Unemployed, cash running out. How to tap into my... Newer »
This thread is closed to new comments.