Do not mess with the dashboard setting below - it should be ON (light blue as shown)
Users are reporting problems after accidentally changing this Tumblr setting. It's relatively new, confusing and very poorly described. For starters, if you turn it off, Post Limit Checker will no longer work. But that may be the least of your problems. You'll have no theme at all. And that applies to everyone - logged in or otherwise. No links, no other pages, no background, no archive - no anything really. It's almost like not having a blog at all. Logged in users can see your recent posts in a generic window on their dash only and everyone else sees nothing.