Are you using prefixes on your database tables?

Look in your files:
/includes/configure.php
/admin/includes/configure.php

1 make sure the database name, username and password match

2 make sure your URLs and paths are the same

3 check to see if you have a Prefix set ... if using a prefix you need to alter the fix for the admin table so that you add the prefix to the statements and build the right database name ...