External monitor turns off when I close my Macbook

Capt. Fred posted a very good support page about how to acheive clamshell mode external displays.

http://support.apple.com/kb/HT3131

Requirements for closed display mode:

• Power adapter
• External keyboard, mouse, or trackpad
• External display

Use these steps to enable closed clamshell (display closed) mode:If you are using a wired keyboard and mouse:

1. Make sure the computer is plugged in to an outlet using the AC power adapter.
2. Connect a USB keyboard and mouse to your computer.
3. With the computer turned on connect the Mac notebook (using the appropriate Apple adapter if necessary) to the appropriate port on the external display or projector and turn the display or projector on.
4. After your computer's Desktop appears on the external display, close the computer's lid.
5. When you close the lid:
   • In OS X Lion and later, the external display will change to a blue screen, then will show your desktop.
   • In Mac OS X v10.6.8 and earlier, wake the computer up by clicking the mouse button or by pressing a key on your external keyboard.

You should now be able to use your Mac notebook as you normally would, with a USB keyboard and mouse.If you are using a Bluetooth keyboard and mouse on a Bluetooth enabled Mac notebook:

1. Make sure the computer is plugged in to an outlet using the AC power adapter.
2. Verify that Bluetooth is turned on by using the Bluetooth pane of System Preferences or the Bluetooth menu icon.
3. Pair your Bluetooth keyboard or mouse with the computer. For step-by-step instructions, see this article forkeyboard pairing or see this article for mouse pairing.
4. In System Preferences, be sure that the Allow Bluetooth devices to wake this computer option is selected.
5. With the computer turned on connect the Mac notebook (using the appropriate Apple adapter if necessary) to the appropriate port on the external display or projector and turn the display or projector on.
6. After your computer's Desktop appears on the external display, close the computer's lid.
7. When you close the lid:
   • In OS X Lion and later, the external display will change to a blue screen, then will show your desktop.
   • In Mac OS X v10.6.8 and earlier, wake the computer up by clicking the mouse button or by pressing a key on your external keyboard.

You should now be able to use your Mac notebook as you normally would, with a USB keyboard and mouse.

Note: If your external display is not recognized when it is connected and the computer is powered on, try connecting the display while the computer is asleep or while the computer is off; wake or power on the computer after you connect the display.

How to disconnect your Mac notebook from the display after use:

For best results it is recommend that you put your computer to sleep before disconnecting your display.

Note: Some DVI and Mini DisplayPort displays—including Apple's aluminum-framed DVI displays and the 24-inch and 27-inch LED Cinema Displays—can be unplugged without putting the computer to sleep. If you aren't sure whether your display supports this feature, put your computer to sleep before unplugging the display.

Opening the internal display while in closed clamshell mode

Opening the display on your Mac notebook while it is in closed clamshell mode will have different results based on the operating system you are running.

OS X Lion and later

If you open the lid of your supported Mac notebook computer while in closed clamshell mode, the display will flicker to a blue screen after a few moments then both displays will become active. Close the lid to return to closed clamshell mode.

Mac OS X v10.6.8 and earlier

If you open the lid of your supported Mac notebook computer while in closed clamshell mode it may appear to have no video. This is expected behavior. When your computer is in closed clamshell mode the built-in display is disabled and all video memory is allocated to the external display for best performance.

To reactivate your built-in display, sleep the computer and then wake it, or use the Detect Displays button in the Displays preferences. You can also use the key combination Command+F1 on keyboards that do not have a Numlock key.

If you close the lid the system sleeps, if you meet the requirements of clamshell mode then it remain awake.

My guess is that your wifi keyboard isn't being recognized to meet these requirements. Try it with a usb or bluetooth keyboard to see if it changes things.

http://support.apple.com/kb/HT3131

Do a PRAM reest http://support.apple.com/kb/HT1379

Dear SmokeMonster,

ups, I posted this text onto another discussion already, sorry, wrong place. (it was with mouse problem). so here it is again: i have the same problem as discussed before - my white macbook is connected to an external display (Samsung LCD), and when I close the lid, I "lose" the big screen as well. maybe it is just some kind of system preference setting - it used to work all right for the past half six months, then since I connected a wireless mouse about two days ago, it is giving me problems. Do you have any good tips? Thanks! MacMester.

I have the same problem but PRAM test doesn't fix it. It is a brand new Macbook Pro with Retina. I have external monitor hooked to it through mini display/DVI converter. It is a 20" DELL monitor. I also have USP mouse and keyboard wired to it. If the computer runs on battery power, as soon as I close the lid, the external monotor suts down and it cannot be awaken. I tried with Bluetooth wireless keyboard and mouse, and nothing changed. However, as soon as I connect the power cable, everything works. I called apple care and they have no idea.

I have read in this forrum all sorts of complaints. Some monitors won't shut down, some won't wake up. Some problems get fized accidentally with seamingly unrelated actitins and some never get fixed. This is rediculous. I wonder what is going to take for this issue to be resolved.

Thank in advance for your help!

RT

Fantastic. This was it. I had reset my PRAM (though I didn't think it was the solution) but I didn't expect it to work because my Macbook Pro works with my cinema at my employer's office. At my home office, my cinema wasn't working.

It turns out all I was lacking was plugging in my Macbook. Thanks!

That's why we're here! 🙂

You might want to consider starting a new discussion. Since this one is marked solved, less people are likely to look at it. You can link to this one.

Thanks. I did that.

Laptop or desktop must be plugged in to power for this function to work.