Every now and then, people report that their MacBook or MacBook Pro's screen has turned blank. Sometimes this happens in the middle of working, but other times when the screen will not turn on after a restart or when waking from sleep. There are several reasons as to why this can happen, some of which are software-related, and others that have to do with the hardware.
The display going out could be a matter of a software configuration problem, either with the display drivers or with one of the active processes that interacts with them, such as the window server. There are a few ways you can overcome this. The first is to change the display configuration by either plugging in or unplugging an external monitor. This will cause the drivers to refresh the display output and desktop configuration; hopefully, this will reset the error. The second way is to try sleeping the system again by closing the lid and opening it. When you close the lid, you should see the battery and sleep indicator lights (green and white, respectively) turn on.
You can also use a key sequence to force the display to sleep and reset, which, hopefull, will force the display to reset properly and turn on. To do this, press and hold the Control and Shift keys, followed by the Eject key.
Lastly, if the display will not work even after rebooting, try loading into Safe Mode, especially if the display turns off after properly showing an initial gray screen. If safe mode works, you will need to troubleshoot the software setup by first uninstalling any recently installed drivers or utilities, and then by creating a new user account for testing purposes, since sometimes display problems can happen from an account-specific configuration problem. This will tell you if the problem is account-related or has to do with more global resources. If the problem persists in a new account, the next best step would be to boot off your Mac OS X installation DVD to see if the display works under a completely bare and fresh installation.
If the installation DVD works, then you will need to reinstall your OS by first reapplying the latest "Combo" update for your version of OS X (this is best applied when in Safe Mode), and then by run the installer from your OS X DVD and ensure that you have "Archive and Install" selected with the option to save user accounts and data (this is done by default in Snow Leopard).
If the display problems occur when booting from the installation DVD, it is likely you are suffering from a hardware malfunction and will need to troubleshoot the hardware setup.
Hardware issues that can affect the display output include firmware settings as well as the display hardware and controllers themselves. Many people have tried to reset the PRAM when they have issues such as the screen being blank when the computer is woken from sleep; however, many display settings are stored in the System Management Controller. Therefore, in addition to resetting the PRAM you may benefit from resetting the SMC on your machine. On most MacBooks you can do this by removing the power and battery, and pressing the power button for 15 seconds, but some models vary so look up how to do this for your particular machine.
Beyond firmware settings, you may have a problem with the display inverter or LED driver board, which is what runs the backlight on LDC displays. When this happens, the display should still be working, but will not be easily visible because of the lack of lighting. You can test this by shining a flashlight on the display at different angles, or preferably through the Apple logo on the back of the display. If you see graphics showing on the display, then your backlight is not working. If a restart or SMC/PRAM reset do not help, you will need to take the computer in for servicing.
Lastly, if you have recently had the computer serviced (especially if done by yourself), some of the display-related circuits may have been improperly connected or insulated upon assembly. Apple has foam and plastic insulation around circuits and connectors that can be shorted out by touching other components, so if you forget to put these back on when assembling the system, you can easily cause a component like the inverter to fail. Luckily this usually can be fixed by replacing the insulation, but you will need to have it serviced again to fix.
If you are unable to get your display working, you can still control your system in an attempt to save your work and safely shut it down. One way is to use Screen Sharing, which you may have enabled in the Sharing system preferences. You can then use Remote Desktop or Apple's built-in Screen Sharing service to connect to and control your Mac.
Alternatively, if you have Remote Login enabled (SSH), you can use an SSH client on any other networked computer to log in and issue the "shutdown -h now" command to close down and turn off the computer. This will take familiarity with the Terminal, as well as knowing its IP address (unless you are on a Mac). Here's the basic procedure:
Launch the Terminal application with SSH support
Type the following command:
In this command, the username is the short account name on the system, and if you are using a Mac "Computer-Name.local" is the computer's network name, such as Tophers-Desktop.local; however, it can also be the computer's IP address.
Confirm connecting and supply your password (it will not be shown)
Issue the shutdown command by typing the following:
sudo shutdown -h now
This process will turn off the system, but will force applications to quit so you will lose unsaved data. However, it still is a better option than pressing and holding the power button to turn off the system.