Hi

When I log in it's no problem with minecraft, and it's no problem to play a new world, but I have problems with one of my worlds. The first time I had the problem it was a black hole in the underground. I tried to restart minecraft and log in to the world again, but when I clicked on the play world button it moved me back to the start again (with the single player and multiplayer buttons). I tried to do everything (change versions, delete minecraft and download it, restart the computer and more) but it didn't work. What's the problem? How do I do?