World's aren't opening

When I click on any world in my computer it doesn't open, not only one, all of my worlds!. I can create a new world but I can't open it after I leave the world. This happened once, I tried to reinstall Minecraft then it worked but this is the second time and when I reinstall Minecraft I lose all my worlds, I don't know what is happening here. When reinstalled it opens but after 3 weeks later it starts to not to open. I installed from Minecraft launcher, I don't want to lose all of my worlds