This error message (404) usually shows up when you enable the Clean URLs option in Drupal.
To solve this issue, the only thing you should do is, to add an .htaccess file (or modify the existing one) inside the root folder of your Drupal installation which will contain the following lines of code:
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?q=$1 [L,QSA]
The code above will only work if mod_rewrite is installed in your Apache server. If you are not using Apache server or you have not mod_rewrite installed then this code will not work and you need to search for the appropriate solution about the server you are using.
