You may run into the problem that links to thumbnails in the media Manager are broken and that sub directories cannot be opened. You want to insert an image, you do see the names of the pictures in the media manager, you can insert the code in your article, but nothing happens. What to do?
The problem lies with the path you have set in the global configuration for media management in Joomla. A mistyped url or one slash too many will result in broken links.
Let's first look at the problem. The image below of the media manager shows the problem. Names of images and subdirectories are show, but the thumbnails of images are not displayed. You can insert the image in an article (the correct code will appear if you look in the html code), but the links are still broken and the image is not shown in the text editor.
Broken Links in Joomla's Media Manager

The answer is fixing the media path in Joomla's global configuration. As default, the Path to the Media Folder is images. If you put a forward slash after images (see the yellow highlight in the image below), the links will be broken. By restoring the default path, you have solved the issue and the thumbnails are show again.
The Default Path is images
