I have this message: Error: 404 Component not found How can I find the missing component?
You can find what is the missing component by either checking what is the component assigned to that specific menu item that creates this page, or if there is no menu item for this page you can disable SEF URLs in the Global configuration and find the name of the component by the option=com_component part of the URL.
option=com_content part means that the component of this page is the Content component.
Configure the "System - Debug" plugin to log category jerror, to show log entries and enable debug in Global Configuration.
Try accessing the missing component. Click on Log messages and it will tell you which component is missing.