Every 60 minutes all laptops will go into sleep mode if they haven't been utilized.  If you depress the mousepad or the spacebar on your keyboard it will wake the laptop up and the login screen appears at which time you log in and the laptop is ready for use.  If for any reason the mousepad or spacebar does not bring back the login screen, hold the power button down long enough for the light on power button to go out.  Wait 30 seconds and depress the power button again until the light on the power button illuminates.  This should restart your computer and bring you back to the login screen.