If you can’t seem to get the magento top categories menu to work (on a variety of themes), here are a few places to check:
1. Make sure you have a root category selected. To check this, go to ‘system > manage stores’, click on the “main website store”. Use the dropdown next to “root category” to select the root category. If you have all your categories as root categories, you won’t be able to display them as the top navigation. An easy way to do this is to add a category for “all” that will contain all products, and move your existing hierarchy underneath this new parent category. Then, just assign “all” as your root category.
2. Make sure the categories themselves are set to ‘active’ in each of their setup pages
3. Make sure the layout for your theme is set. If you used “add design change” to add your magento theme, you shouldn’t have a problem with this. But, you may need to duplicate the entry for “skin/css” if you used the “configuration > general > design” route. Most magento themes will have elements for “templates”, “skin (images / CSS)”, and “Layout”, but some may not need “Translations” or “Default”.