I had this problem. (but it was not caused by changing themes or anything related to the theme)
I was making a new post, then trying to upload a picture from my hard drive through the upload media window- the picture never would upload, though it was a small file. So I closed the window and went back to the draft I was working on. I clicked save draft and then the draft disappeared. I then went to the EDIT POST navigation page and No posts are listed. Also no pages are listed. I get a page not found error when I try to go to one of my pages from a google search.
Went to Hostgator support for help. My tech said,
“This is a common occurrence with wordpress sites in general. You can repair a database within cPanel by going to MySQL Databases and selecting the wordpress database involved and clicking repair.”
Then he repaired it for me and all my posts and pages came back except the one that I was working on when it happened.
