It's probably a problem of settings but I cannot figure out what I did. Each time I add a new object in my scene, it shows up on the scene and it is rendered but it doesn't show up on the outliner list. Which is a bit annoying, I like to keep things tidy. If I reset to factory setting, and duplicate the starting cube, I finally have two cubes in my outliner. But even after reseting the setting, the problem is still here when loading my original scene. Any hints?
Edit: I added a screenshot, in the outliner menu, only the cylinder is displayed.