So, my primary world won't show up in the list anymore. Please help?!

I was en route to a distant nether portal in my favorite world when my laptop died. I plugged it in, restarted it and tried to get back. but my world isn't showing up with the rest of them. I've been building in this world for over a year and it's the only one I really care about using. Does anyone know what happened or how to fix it?!

Also, the world is showing up in my .minecraft folder, but not in Minecraft its self.