There can be 2 reasons  1. Machine not going to sleep after closing the LID : Open control panel > power options > What does closing the LID do : Choose Sleep  2. Open Start > settings > account > sign in options    [IMAGE]  
Latitude 5400 doesn't show a lock screen after opening libs. Normally, we should be able to go to lock screen after opening libs but when I close my laptop and then after some hours open my laptop it won't show the lock screen and the content of my laptop is available for anyone which is not secure.   Is there any solution for that?
Latitude 5400 doesn't show lock screen after closing libs