Getting default (not CI) 404 for all pages - codeigniter

Question

I am trying to develop using CI for the first time. I have not changed any defaults WRT paths, .htaccess, etc. Two hours ago I was able to load pages; now I am not. All of this is on a virtual box running on my Mac, and I had been messing with the virtualbox settings in order to try to get the web pages to load while connected to a VPN (did not succeed). At no time did I edit any files on the VM, whether for connect settings or related to CI and my project.
Giving up with the VPN, I returned to my project to continue with code enhancements. Only now, as my title suggests, nothing will load. The default "It works" page loads so I know nginx is responding to requests. I don't get the Code Igniter 404 page -- I get the generic:
Not Found
The requested URL /index.php/c_login/ was not found on this server.
In this example, c_login extends CI_Controller and displays a view in its index function.
Based on my searches:
My config.php contains $config['uri_protocol'] = 'REQUEST_URI';
There was no .htaccess file previously, and that is still the case
I don't understand the bit about capital first letter in my controllers, as I've had lower case since I started the project and had no problem
Except for a minor change to a view file (not trying to load that one right now), nothing has changed since the last pull from the git server
I had left the welcome_message view and welcome controller in place when starting this project, and that no longer works either. Any ideas? I am at a complete loss.

Answer 1

Change this
In your config.php
$config['base_url'] = '';
$config['index_page'] = '';
$config['uri_protocol'] = 'AUTO';
then in .htaccess(this should be place out side of application folder)
RewriteEngine on
Options -Indexes
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php/$1 [L]
EDIT 01
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php/$1 [L]