Navigation disabled when adding menu items

I have 2 top level menu items in main navigation: “Chinese” and “English” which are custom links that have underneath each sub-pages and sub- sub-pages. I now want to add 2 more menu labels (both existing pages) to the top level in addition to “Chinese” and “English”. When I do this and save menu and view site, the entire navigation is disabled, I see only white vertical lines where navigation should be. I tried adding one at a time, I also tried creating custom links and adding those to menu for the 2 new labels instead of pages, same problem. I go back to edit menu and the 2 things I added are gone. Also the main navigation ballot box at the bottom keeps getting unchecked regardless my checking it. What’s wrong? Any feedback is appreciated. Thank you.