Display main menu vertically (Drupal. 7.9)
You need to use Firebug and find the style rule that is being applied to the &lt;li&gt;elements that will be displaying them inline. Firebug will tell you where the CSS is being loaded and this will lead you to the culprit. One tip is to make sure you're not aggregating CSS so you can find the correct stylesheet. If it isn't theme specific it may be CSS being loaded by a module, but I am confident that there is some CSS there that is creating the result you're seeing.