Second Install...

Are you using the same database, If yes thats why the same

Are you using the same database PREFIX for the second installation? If so, it will connect to you "old" sites database.

Well the configuration didnt show up at all : / i just uploaded the files into the subdomain folder and thats it. Looks like it configured the SQL its self, or it recognized the files : / hehe

Go to domain.com/sub/setup.php

its problem of prefix, make sure what they not same, to see it, open in your root directory (first page) config.php and you will see following:

<?php
// database settings
$db_host="localhost";
$db_user="username";
$db_pass="database password";
$db_name="database name";
$db_prefix="fusion_";
define("DB_PREFIX", "fusion_");
?>

Now pay attention to following lines:
$db_prefix="fusion_";
define("DB_PREFIX", "fusion_");
and what between " and " tags, now check it witch your new (sub domain page (new page)) config.php Check if they are same, if they are same what means what you need to change your second page database prefix, because i created 3pages in one database, and all was fine.

You should try installing from the begining as Elactos mentioned at above

Be sure, that you renamed the blank_config.php to config.php!!
If you did not do it, then the config of your first site will be used!