Minecraft does not load my worlds

I wanted to start minecraft and I saw that there was a new launcher.
I started minecraft but it did not load my world. It just stayed on the loading screen. When I click another time it says that minecraft isn't reacting. Now I can play minecraft ):

What I expected to happen was...
That minecraft would work

What actually happened was.......
Minecraft did not load my world

steps of reproduce:
1. click on minecraft
2. When the launcher is downloaded click on play
3. When minecraft has started click single/multiplayer
4. Notice that the world does not load but stays on the loading screen.