I can't load or create world

A few days ago, I couldn't launch the game. I found that I needed to add " -Xss1024K". So now I can launch it, but I can't load or create any world, it keeps telling me "Loading world, Preparing spawn area : 96%". I waited 40 minutes, without success. And also, when I click on "Singleplayer" the game freeze a lot longer that he does usually. Can you help me ?