If an application on your Mac isn't working properly, you might want to reboot the computer to see if that solves the problem. You may also need to reboot your Mac after installing a new application or a software update. You don't need a disk to reboot your Mac-you can accomplish this by selecting a command with your mouse, or pressing keys on the keyboard.
Step 1: Click on the Apple icon at the top left of the screen with your mouse, then click "Restart." A dialog box will appear, asking whether you are sure you want to restart your computer. Click "Restart" in the dialog box. Before restarting, the Mac will quit all applications. Any applications that are running will prompt you to save changes to open documents. The Mac will shut down, then reboot automatically.
Step 2: Press the "Control," "Command" and "Eject" keys simultaneously if you want to use the keyboard to reboot your Mac. This command will quit all running applications after prompting you to save changes in any open documents, and then the Mac will reboot.
Step 3: Press the "Power" button on your Mac and hold it for at least five seconds to reboot if your system is frozen and you are having trouble rebooting using the mouse or keyboard. You will not have an opportunity to save any open documents using this method.
Step 4: Unplug the Mac's power cord from the wall if you are unable to reboot using the first three methods. Plug the power cord back in, then press the "Power" button to reboot.