Sometimes when there is a glitch in the windows, the mouse was not working. you have to use the keyboard to restart windows. do this:
Win key or Ctrl + Esc to start the Start menu.
After that press U to select the Shutdown command. (For windows xp) or use the right arrow key (for Windows 7).
use the arrow keys up / down to select the Restart.
press the enter key to continue.
if you have not saved the document file is opened, Windows will remove the instructions for your first save. press the Enter key to save the file unsaved document.
sometimes when restarting, the computer take too long to work again. To make sure windows is repairing itself, see the hard disk indicator light. if the flashing lights mean the computer still works and if does not go on or stay on, most likely your computer has hang.
You have to be patient because when Restart your computer may take longer than usual due to windows trying to find the problem and fix itself.