Categories are not showing

Hello friends;

I am running my wordpress 2.7.1 blog on a custom domain http://www.pakzilla.com. And I noticed that my categories stop showing in side bar. Some times its also disappear from my dashboard too. But now I can see them. And all of posts gone uncategorized. If I edit post to assign category to it then in Categories pane I cant see any category in All Category tab, but Most Used tab shows all categories.

I hope my issue has been understood, and I hope to get useful pointers to identify this problem.

Tahir