Drop existing WP install and install a new clean WP

newinstall.php

<?php
/* Place the file into WordPress root folder and open the file in your browser. */

/* Settings */
define( 'BLOG_TITLE', 'WordPress Dev' );
define( 'USER_NAME', 'admin' );
define( 'USER_EMAIL', 'foobar@example.com' );
define( 'USER_PASSWORD', '123456' );
define( 'WP_SITEURL', 'http://wp.dev' );

/* Init */
if ( ! defined( 'ABSPATH' ) )
	define( 'ABSPATH', dirname( __FILE__ ) . '/' );

require_once( ABSPATH . 'wp-config.php' );

define( 'WP_INSTALLING', 1 );
require_once( ABSPATH . 'wp-settings.php' );

/* Delete Tables */
global $wpdb;
$tables = $wpdb->get_col( 'SHOW TABLES;' );
foreach ( $tables as $table )
	$wpdb->query( "DROP TABLE IF EXISTS {$table}" );

/* Install WP */
require_once( ABSPATH . 'wp-admin/includes/upgrade.php' );
$result = wp_install( BLOG_TITLE, USER_NAME, USER_EMAIL, true, '', USER_PASSWORD );


if ( true == is_blog_installed() ) {
	/* Login */
	$creds = array();
	$creds['user_login'] = USER_NAME;
	$creds['user_password'] = USER_PASSWORD;
	$creds['remember'] = true;
	$user = wp_signon( $creds, false );

	/* Redirect */
	if ( ! is_wp_error( $user ) )
		header('Location: ' . $result['url'] . '/wp-admin/' );

} else {
	echo '<pre>';
	var_dump( $result );
	echo '</pre>';
}