I am not certain, but I think what you have going on there is something like index.html rather than index.php. If so, I believe this .htaccess might help:
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
### Extra Options
## choose for default.html
#RewriteRule . /default.html [L]
## choose for index.html
#RewriteRule . /index.html [L]
## choose for WordPress index.php
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
That last line directs your domain to run index.php:
<?php
/**
* Front to the WordPress application. This file doesn't do anything, but loads
* wp-blog-header.php which does and tells WordPress to load the theme.
*
* @package WordPress
*/
/**
* Tells WordPress to load the WordPress theme and output it.
*
* @var bool
*/
define('WP_USE_THEMES', true);
/** Loads the WordPress Environment and Template */
require( dirname( __FILE__ ) . '/wp-blog-header.php' );
