Changes to your blog can cause the links in the Navigation Bar displaying below the banner to no longer work. Some common causes of broken links in the Navigation Bar are:
Links go to error or blank page.
The most common cause of links in the Navigation Bar being broken is a change to the Domain Name, Folder Name, or Domain Mapping.
Links in the Navigation Bar and Blog Footer will not automatically update with changes to the URLs for your blog's content.
To fix the links, go to Design > Content and click 
to open the Navigation Bar Configuration pop-up box. Update the URLs for the links, click OK, and click Save Changes to update your blog.
Links refresh or go to home page.
When clicking the links in the Navigation Bar just returns you to the front page of your blog, it is a sign of the banner link overlapping the Navigation Bar. This commonly occurs when Custom CSS is used to add or edit the banner image.
The #banner-header a element of the CSS needs to have the correct banner height defined to prevent the banner link overlap.
To define the banner link height, go to Design > Custom CSS and include the below code:
#banner-header a { height: XXXpx; }
Replace "XXX" with the exact height of your banner image and click Save Changes to update your blog.
Additional information is available in the configuring the Navigation Bar article.