What's wrong with my Minecraft server?

I've spent months building a server with everything I want in it, but when I updated it to 1.7.4, the entire world was deleted. Everything was lost, I have no items, and all of my mods disappeared. How do I get everything back?

This happened to me before. It baffled me, didn't know why. I think it has to do with the source code being changed so much between versions that it had to create new biomes, etc. Try opening your properties file and change the document to your original files. I had to go back and set my world to the world I wanted. Because the biomes aren't in your old map, they haven't been able to create it without ruining it. If you made a back-up, you can run from the back-up. I always make a back-up just in case when it comes to making any changes on my server. Your mods may be world specific depending on your plugins and permissions. They may come back once you get the world to come back