Save & Close Open Documents: If possible, save and close all open documents in all running applications. You can quickly see which applications are running by looking at your Dock – any application icon with a small, black dot below or beside it is still running.
Quit Running Applications: Next, quit all running applications except the Finder. (You can't quit the Finder anyway.) Select them one at a time and press [Command] + [Q].
Force Quit Unresponsive Applications: If any running applications refuse to quit i.e. they seem “frozen,” then force them to quit. To force an application to quit, right-click on its application icon in the Dock. In the menu that appears, select Force Quit. Alternately, press [Command] + [Option] + [Esc], select the application in the window that appears, and click the "Force Quit" button.
Restart The Computer: Select "Restart" from the Apple menu in the top left corner of the screen and then, when prompted, click the [Restart] button. This will also log you out.
If Necessary, Force The Computer To Shut Down: After a few moments, the computer should restart. If it doesn’t restart after a minute, or so, press and hold the power button on the back of the computer until the computer powers down.
Check Cable Connections: Verify that the power and Ethernet (network) cables are securely attached to the back of the computer and to the wall jacks under the desk. Verify that the mouse and keyboard are both securely connected to a USB port either on the keyboard or on the back of the computer. Verify that the video/projector and audio cables (if applicable) are securely connected.
Turn The Computer Back On: If necessary, press the power button on the computer to turn it back on.
Log Back In: When the login prompt appears, log in as usual and attempt to continue your work.
TROUBLESHOOT A PRINTER PROBLEM
Follow The Troubleshooting Steps For Computer Problems: Sometimes a printing issue is really a computer issue. Always follow the steps above to Troubleshoot a Computer Problem first and then try printing again.
Look At The Printer's Indicator Lights Or Display: These will vary from printer to printer. Look closely at the front or top panel of the printer for lights or displays indicating any of the following:
Online Status: Is the printer "online" and "ready" to receive print jobs?
Ink or Toner: Is the printer letting you know that it needs ink or toner?
Paper: Is the printer letting you know that it needs paper? Check the paper supply in all of the printer’s input trays. You may have accidentally specified a paper feed source that’s empty, such as the manual feed tray.
Instructions: Is the printer asking you or another lab user to take some action, such as insert a sheet of paper in the manual feed tray or clear a paper jam?
Processing: Is the printer busy processing a print job? In the case of a networked printer, it could be someone else’s print job. If the job is unusually large or complex, it may take some time to print.
Check Connections: Some lab printers connect to a computer with a cable. Depending on the printer, this might be a USB or Ethernet cable. Verify that the cable is firmly connected at both ends. Networked printers should be connected to a port on the wall via an Ethernet (network) cable.
Delete The Current Print Job: If the printer’s front/top panel indicates that it’s processing a job or displays an error, try deleting the current print job:
Some printers have a "cancel job" button on their front/top panel. Use this button to delete the current print job.
To delete jobs sent to a printer that’s directly connected to your computer via a USB cable, click the printer's icon in the Dock to open the print monitor window, select the current print job and click the Delete button in the toolbar.
To delete jobs sent to a networked printer, visit the FAQ page and follow the steps in the topic titled "How do I cancel the current print job on a lab laser printer?"
Turn The Printer Off Then Turn It Back On: Turn the printer off for a full minute and then turn it back on. Wait for it to start up to an online and ready state, and then try printing to it again.