Re: the connection of db
When you run tiki-install.php it asks you for database connection details. These then get written to the /db/local.php file. In TikiWiki 1.7.X and below this could be saved in /db/tiki-db.php, but in TikiWiki 1.8 and above this is no longer possible. Sessions require and look for local.php
You may want to delete /db/local.php and try again. Make sure that your PHP is setup with the correct database module too. If your on shared hosting or want your tiki hosted, take a look at TikiFriendlyHosts
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