Hi,
Go to Site Actions > Site Settings > Site Collection features. On site features, check if the feature 'SharePoint Server Publishing Infrastructure' is enabled. If enabled, disable the feature.
On disabling the publishing feature, you would see the top link bar page in navigation.
If you want publishing feature to be enabled, you can change the top navigation from 'Navigation' page in site settings. SharePoint out-of-box sites can be configured to Show pages and sub-sites. To enable shows pages and sub-sites, click on the Site Actions > Site Settings > Modify All Site Settings. On the Site Settings page under Look and Feel click Navigation to access the Site Navigation Settings page.
I hope, it helps.
Cheers ...
Rajendra Shekhawat