I've used paragraph styles in Indesign CS4 since 2009 and yesterday (6-10-14) I noticed the paragraph styles dialogue was empty. I figured somehow I must have accidentally deleted or cleared them. I then proceeded to attempt loading them from another document. After "Loading Paragraph Styles..." via the drop-down in the upper right corner of the dialogue box nothing showed up.
I then proceeded to create a new style it to never appeared in the list—it remains empty.
Replacing the preferences fixed the issue.