Content list empty to Administrator
From the screenshot you show, it's clear that you installed and enabled the Administration Views module. In fact, for a fresh Drupal 7 installation, the admin/content page would appear as in the following screenshot.


  


I installed it on my test, and it works fine for me.


  


Once you install and enable the module, that administrative page is replaced from a view. If you changed the view, it could be it is filtering out the nodes to show in that page.
Go to admin/structure/views/view/admin_views_node/edit and check the filter criteria aren't too much restrictive. By default, that view has only exposed filter criteria; if you find any not-exposed criterium, that is something manually added to the view, and it could be causing the issue you are seeing. A filter for the content type can cause what you see, but so a filter for the creation date, and many other filters. 

As reference, this is the setting page for the view as it comes after installing the Administration Views module.


  


Also, the view has a setting for caching it (as any view); if it has been changing from None to Time-based, then either the query results or the render output could be cached for too long. The default values are 1 hour for both.


  


The other reason could be that the view is being filtered by the author name. If I put three spaces in the Author field, and then I click Apply, I get the following.


  


Now the list says No content available. even if I still have those two nodes you saw in the previous screenshot. That is because the author name doesn't contain three spaces.
The same happens if I enter three spaces in the Title field.  

To be sure the exposed filter criteria aren't causing any issue, click on the Reset button right to the right of the Apply button. That will reset the values for those filters.