My laptop battery died before I was able to save and close the game. Now when I start Minecraft, my game is not listed. I can see the folder of my game in Windows Explorer. How do I get Minecraft to open that game again?
It seems like the file is corrupted. You can still see the file because it still exists, but you can't access it. First of all, back up your files often, so this doesn't happen. Within the saves folder, copy the save, and rename it to "New World". Then, go into Minecraft and create a new world called new world. It won't completely be fixed, but it should recover some of the data.