kwbridge on "Always Getting 404 Not Found Error !"

Whenever I want to go to a page or a post, it shows me this !
What can be the problem ? Please help ! ASAP !

Screenshot :
https://s31.postimg.org/rszzkb0nv/Untitled.png

Can you login to the admin? Try saving the permalinks under Settings > Permalinks. You don't need to change them - just save them.

And if that doesn't work does switching to the default permalinks correct the issue?