Admin bar missing from published site

My admin toolbar doesn’t show on my site when I’m logged in. It will show when I preview posts but not on the published site. I am using WordPress 3.5. I think this problem started before I upgraded, though.

I have tried:

1. Switching to Twenty Twelve and Twenty Ten themes. No effect.
2. Deactivating all plugins. No effect.
3. Checking that the Show Toolbar setting in my user profile is checked.

I noticed the 28px margin-top style embedded in wp-includes/admin-bar.php isn’t registering on the published pages. But I’m not sure what that means.

Thanks for any help you offer.