Question :

In my office, I am using an external monitor as my main screen for my MacBook Pro. Today, the screen didn’t respond when I connected my MacBook however : the screen stays black and nothing appears on-screen. So I opened up my MacBook and used the built-in screen to figure out what’s wrong, but so far I haven’t found any indication in the Displays Preference Panel that my MacBook even detects the second screen…

What can I do ?

Answer :

In such situations you should always do this first :

Remedy #1 :

• if you are using a MacBook, MacBook Air or MacBook Pro, make sure you have the power adapter connected
• if your laptop is on battery power, the external screen will go black whenever you close the lid of your laptop (when on battery power, all connections are powered off when you close the lid to save energy)

if this works, you’re good, if not, try Remedy #2

Remedy #2 :

• make sure your monitor is switched ON
• then hit the SPACE-bar on your external keyboard several times (maybe once, usually about 5 to 10 times…)
• the monitor should now appear and show the inlog panel to unlock your screensaver
• then login

if this works, you’re good, if not, try Remedy #3

NOTE : if you have a Benq monitor (especially the BL2420TP), try this first :

fixed : Benq monitor stays black when MacBook is switched on

Remedy #3 :

• unplug all cables between the monitor and your Mac ( DisplayPort / Thunderbolt / HDMI / DVI / VGA  and also USB, UTP, FireWire and PowerAdapter )
• shut down your monitor
• shut down your MacBook
• reconnect all cables and double-check if they’re properly connected on both the Mac and the monitor
• switch on your MacBook
• switch on your monitor

if this works, you’re good, if not, try Remedy #4

Remedy #4 :

• on your MacBook, open Apple [main menu bar top-left] –> System Preferences
• in the System Preferences window, select “Displays”
• in the Display Preferences window, see if there is a button marked “Gather Windows” bottom right
• if there is no “Gather Windows” button, press the ALT-key on your keyboard and a button marked “Detect Displays” appears ; click on it when it appears

if this works, you’re good, if not, try Remedy #5

Remedy #5 :

• on your MacBook, open Apple [main menu bar top-left] –> System Preferences
• in the System Preferences window, select “Displays”
• in the Display Preferences window, see if there is a button marked “Gather Windows” bottom right
• if there is a “Gather Windows” button, click on it
• then you will see 2 Display Preference windows on your MacBook screen
• select the Display Preference window that has 3 tabs on it marked “Display”, “Arrangement” and “Color” (not the window that has “Display” and “Color” only)
• first, press the ALT-key on your keyboard and a button marked “Detect Displays” appears where the “Gather Windows”-button used to be ; click on it when it appears
• if your monitor switches on, you’re good, if not…
• click on the “Arrangement”-tab and in the next window put a checkmark at “Mirror Display”
• if your monitor switches on now, uncheck the “Mirror Display” option again and close your MacBook… you should be good now…

if this didn’t work, try Remedy #6

Remedy #6 :

• unplug all cables between the monitor and your Mac ( DisplayPort / Thunderbolt / HDMI / DVI / VGA  and also USB, UTP, FireWire and PowerAdapter )
• shut down your monitor
• shut down your MacBook
• reconnect your Mac to your monitor using a different type of cable then you normally would choose (e.g. if you normally use a DisplayPort/Thunderbolt-cable, use an HDMI or DVI cable now)
• switch on your MacBook
• switch on your monitor
• if your monitor wakes from sleep now, open Apple –> System Preferences
• in the System Preferences window, select “Displays”
• in the Display Preferences window, see if there is a button marked “Gather Windows” bottom right
• if there is a “Gather Windows” button, click on it
• then you will see 2 Display Preference windows on your MacBook screen
• now, remove the monitor-cable that you have just used to connect your MacBook to your monitor
• then, reconnect your MacBook to your monitor using all cables you normally use to connect the two
• if your monitor now wakes from sleep, you’re good
• if it doesn’t, restart your monitor
• it that doesn’t help, restart your Mac

normally your issue should be resolved by now…

if still the monitor stays showing a back screen, I’m sorry to inform you that your screen probably has a hardware problem… if so, get an authorized Mac-repair-centre to fix it, get the Apple Store support-crew to fix this…

that’s it !

enjoy 😉