Well, this just happened to me!
I installed joomla but forgot what was the admin password 😦
So i took the installation folder from the joomla zip file and place it in the just installed joomla folder. Then i delete configuration.php file from joomla folder. then it is done. went to joomla application by my web browser and found the installer again 🙂
If needed, delete your database. (just a precaution )