No duplicate of production site

babipanghang, thanks for your comment. I just did that, but still no solution. Could it be the settings.php file? Is there anything else that I may need to change or add on the settings.php file besides what Roadrunner mentions? Like Roadrunner instructs, I just copied my sites directory over to replace the testsite/sites directory created by fresh install, and then I changed settings.php in testsite/sites/default directory to point to my new database. BTW, my testsite directory is right on the root directory, what I changed in the database section of the settings.php file under testsite/sites/default is just the two lines below the "Database URL format" portion, see next:

* Database URL format:
* $db_url = 'mysql://username:password@localhost/databasename';
* $db_url = 'mysqli://username:password@localhost/databasename';
* $db_url = 'pgsql://username:password@localhost/databasename';
*/
$db_url = 'mysqli://usernewdatase:passwordnewdatabase@localhost/newdatabasename';
$db_prefix = 'newdatabaseprefix';

Other than these I have not changed anything else, everything else in my settings.php file from remains the same since I made the backup copy of all my production site from the server onto my computer. Now, the one thing I notice is that the format of my database starts with mysql, but the format in the new settings.php created by the fresh Drupal is mysqli, and I just replaced the values (username, password, and databasename), not the whole line. Does this matter?

Thanks!