Please check http://localhost/xampp/status.php
to make sure that MySQL is running, then if it is, make sure your firewall isn't blocking it.
About the "Connection for controluser as defined in your configuration failed." error:
Edit "xampp\phpMyAdmin\config.inc.php" and fix the lines that say
/* User for advanced features */
$cfg['Servers'][$i]['controluser'] = 'pma';
$cfg['Servers'][$i]['controlpass'] = 'PASSWORD';
replacing "PASSWORD" with the password of the pma account. The pma account should have all privileges in the phpMyAdmin database.