Broken link problem?

I’ve shot myself in the proverbial foot! I looked at changing my URL, but something went wrong and now I cannot get back into my WP to change it back. I have lost the link to my database and don’t know what to try next! I have tried a back-up, but it did not get me back to the original state.
If I’ve really screwed up can someone please tell me? Or if there’s a fix I’d love that as some of the new pages in my database were about to be copied to the real site…

Thanks in advance.
Derek

My admin url was: http://derek40.com/branch8/wp-admin Now when I type that the dashboard opens, but selecting any item results in a downloaded file. I’ve also tried variations using branch8.derek40.com/ with and without …/branch8 (see final data below for the different Host name)

Selecting the name (Branch8 test) yields a downloaded file called ‘download’ no suffix which contains:
<?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(‘./wp-blog-header.php’);
?>

Other data collected as evidence is:

Host name: branch8.derek40.com
Database: branch8
“MySQL 5 database”
Server: branch8.derek40.com Database: branch8
MySQL branch8.derek40.com
MySQL
• Server: branch8.derek40.com via TCP/IP
• Server version: 5.1.39-log
• Protocol version: 10
• User: derek40@173.236.148.209
• MySQL charset: UTF-8 Unicode (utf8)
Web server
• Apache
• MySQL client version: 5.0.51a
• PHP extension: mysql