I have flagged this post to be moved to the Wordpress forum, you will find more answers there, tho we may need a few more details as to what you are actually doing.
Generally, however WP themes ( your sites behaviour ultimately depends on the theme that you are using).
When you say you can't publish, do you mean the dashboard actually wont let you PUBLISH your post, or that you have multiple post in a category, but only one is displayed.
If you have mucked around with your theme pages.... make sure your LOOP is intact. The loop is that if have_posts(), while have_posts(), the_post() part of the code. If you have no loop then WP can only display one post no matter what you do.