NooTriX

Check the error.log file in your wp-admin folder. If it’s too big (mine was more than 1GB), just delete it and try to access to broken parts of your site, it will recreate the file with the most recurrent error messages.

Finally found the root cause. There was a broken table in the database. Repairing it using phpmyadmin fixed all problems I had been encountering ??

I tried to insert an image into a post, and I noticed that the src attribute of the html tag is empty:

<a href="https://nootrix.com/wp-content/uploads/2015/03/terminatorLike3DPrinting.png"><img src="" alt="terminatorLike3DPrinting" class="aligncenter size-large wp-image-4083" /></a>

Does not work for me. I reverted to twenty fourteen them, inactivated all plugins, re-installed 4.2.1, but still having the same issue ??