Sometimes after installing joomla and playing a little bit around… many of you want to backup the site as a fresh install. Obviously most of users basically do a fresh install. But yes there is another way to do the things in a manner without installing the joomla once again!
Follow the steps below to get it going.
Download a copy of the joomla version installed on your site from www.joomla.org
This will obviously be a zip file… so extract it.
Now, go under the extracted folder get to this path /installation/sql/mysql/sample_data.sql
This is the file which has the sample data in SQL format.
To get this file going… you will need to have access to phpmyadmin for your hosting.
Open this file up with either a text editor or html editor. (both will work)
Now, this is the most important step. All the tables will be as having prefix jos_ but your current joomla site might have it with jos_ or whatever you did while installing joomla. ( you can fine it in your configuration.php file and also in the global configuration tab in your joomla administrator.
Now replace all those jos_ with you jos_ or mos_ or what you have with your joomla install. Yu can do it by pressing Ctrl + H for notepad (find and replace) and Ctrl + F for Dreamweaver.
Once done! Get to your phpmyadmin drop all the tables and import this sql file.
The last step… your admin will not have any password now. Here is a tutorial on how to change your joomla administrator password via phpmyadmin.
Source: jm-tutorials.com/blog/4-technology/65.html (Unfortunately the site was loaded with malicious software when checked last...a long time ago!)