The Requested URL Not Found on Server
Error code 404 means that the URL which we are trying to open was not found on the server and therefore cannot be opened. This could possibly mean there is a problem with Drupal installation or its configuration.
The first thing you might need to do in order to troubleshoot this issue is to check whether it is being caused by some faulty directive in .htaccess file. The best option would be just to rename .htaccess file to something like htaccess and check if you are able to access the website. If it is opening without 404 error, this means you have a problem in .htaccess file. To find out which exactly directive have caused this issue, you might need to go through every line of .htaccess file and comment them one by one and checking website for any errors.
If it is not related to .htaccess file, one of the trusted methods in resolving such problem is to edit file “settings.php”. More specifically, find a line with a variable “$base_url” and uncomment it. Also, make sure to set its value to Drupal installation URL. In most cases it should help to get away from 404 error message when trying to access the website.