Unfreeze your PC

If your PC freeze or stop responding,press and hold down the Ctrl and Alt keys and Delete key.Click Task Manager if the task manager window does not appear by default,and then inspect the list of running applications.If any is indicated as "not responding",highlight it and then click the End Task button.If this doesn't unfreeze your PC,press Ctrl and Esc before you reach for the on/off switch.Sometimes this key combination will activate the Start menu,from which you can safely shut down.