3.7.5 to 3.8.0 Joomla after update of Joomla is shot on several Web space the installation with adventurous errors, such as:

Fatal error: indicated declare class JInput, because the name is already in use in /homepages/43/d40530963/htdocs/v3/libraries/fof/input/jinput/input.php on line 39

Also in various forums entries of other users can be found to do so, such as in:

https://Forum.Joomla.de/index.php/thread/4381-update-fehlgeschlagen/

Before you install the update, you should always perform a full (non-incremental) backup via the Plesk backup manager and then install the update!

We had something already in Joomla 3.2:

https://blog.1awww.com/2013/11/13/Dringende-Warnung-VOR-update-auf-Joomla-3-2/