Not to worry ; it some time happens the simple solution is you have to choose both login screens such as face detection and also username/password screen.Some this will happen because of light detection in the screen ,if you have save your settings at morning the detection may fails in the evening so the better solution is that use both screen.As envioronment changes affects the light also ,so straight your face infront of webcam.
For more solution follow these steps :-
1)Press window button and r (window+r).
2)Run window open.
3)Add cmd in the text box to open command prompt.
4)Cmd prompt window open.
5)Type explorer as command and press enter.
6)The Window Explorer open.
For more solution follow these steps :-
1)Press window button and r (window+r).
2)Run window open.
3)Add cmd in the text box to open command prompt.
4)Cmd prompt window open.
5)Type explorer as command and press enter.
6)The Window Explorer open.
Other solution:-
1)Press Altr +Ctrl+Del to start task manager.
2)Click on task manager.
3)Click new task button.
3)Type explorer.exe in the text box and press ok .
4)Window explorer get open.