Plesk Applications Magento - access denied user issue

[oviliz]

I custom installed Magento from Applications inside Plesk (12.0.18 Update #13) and everything was fine (I don't want to mention the issues with nginx that I then removed...).
Then I delete, still from Applications inside Plesk, that Magento installation.

After that when I tried to create another installation (in the same location), for Plesk point of view was fine. But when I checked my Magento home/admin page it shows me:

There has been an error processing your request
Exception printing is disabled by default for security reasons.
Error log record number: 221074589554

I renamed the root/errors/local.xml.sample to local.xml . That's then the home page (and each other one) looks:

There has been an error processing your request
SQLSTATE[28000] [1045] Access denied for user 'magento_7'@'localhost' (using password: YES)

Trace:
#0 /var/www/vhosts/mydomain.com/httpdocs/magento/lib/Zend/Db/Adapter/Pdo/Mysql.php(109): Zend_Db_Adapter_Pdo_Abstract->_connect()
#1 /var/www/vhosts/mydomain.com/httpdocs/magento/lib/Varien/Db/Adapter/Pdo/Mysql.php(320): Zend_Db_Adapter_Pdo_Mysql->_connect()
#2 /var/www/vhosts/mydomain.com/httpdocs/magento/lib/Zend/Db/Adapter/Abstract.php(460): Varien_Db_Adapter_Pdo_Mysql->_connect()
#3 /var/www/vhosts/mydomain.com/httpdocs/magento/lib/Zend/Db/Adapter/Pdo/Abstract.php(238): Zend_Db_Adapter_Abstract->query('SET NAMES utf8', Array)
#4 /var/www/vhosts/mydomain.com/httpdocs/magento/lib/Varien/Db/Adapter/Pdo/Mysql.php(428): Zend_Db_Adapter_Pdo_Abstract->query('SET NAMES utf8', Array)
#5 /var/www/vhosts/mydomain.com/httpdocs/magento/app/code/core/Mage/Core/Model/Resource.php(169): Varien_Db_Adapter_Pdo_Mysql->query('SET NAMES utf8')
#6 /var/www/vhosts/mydomain.com/httpdocs/magento/app/code/core/Mage/Core/Model/Resource.php(110): Mage_Core_Model_Resource->_newConnection('pdo_mysql', Object(Mage_Core_Model_Config_Element))
#7 /var/www/vhosts/mydomain.com/httpdocs/magento/app/code/core/Mage/Core/Model/Resource/Db/Abstract.php(320): Mage_Core_Model_Resource->getConnection('core_write')
#8 /var/www/vhosts/mydomain.com/httpdocs/magento/app/code/core/Mage/Core/Model/Resource/Db/Abstract.php(350): Mage_Core_Model_Resource_Db_Abstract->_getConnection('write')
#9 /var/www/vhosts/mydomain.com/httpdocs/magento/app/code/core/Mage/Core/Model/Resource/Db/Abstract.php(335): Mage_Core_Model_Resource_Db_Abstract->_getWriteAdapter()
#10 /var/www/vhosts/mydomain.com/httpdocs/magento/app/code/core/Mage/Core/Model/Resource/Db/Abstract.php(360): Mage_Core_Model_Resource_Db_Abstract->_getReadAdapter()
#11 /var/www/vhosts/mydomain.com/httpdocs/magento/app/code/core/Mage/Core/Model/Resource/Db/Collection/Abstract.php(134): Mage_Core_Model_Resource_Db_Abstract->getReadConnection()
#12 /var/www/vhosts/mydomain.com/httpdocs/magento/app/code/core/Mage/Core/Model/Config.php(1353): Mage_Core_Model_Resource_Db_Collection_Abstract->__construct(Object(Mage_Core_Model_Resource_Website))
#13 /var/www/vhosts/mydomain.com/httpdocs/magento/app/code/core/Mage/Core/Model/Config.php(1385): Mage_Core_Model_Config->getModelInstance('core_resource/w...', Object(Mage_Core_Model_Resource_Website))
#14 /var/www/vhosts/mydomain.com/httpdocs/magento/app/Mage.php(491): Mage_Core_Model_Config->getResourceModelInstance('core/website_co...', Object(Mage_Core_Model_Resource_Website))
#15 /var/www/vhosts/mydomain.com/httpdocs/magento/app/code/core/Mage/Core/Model/Abstract.php(208): Mage::getResourceModel('core/website_co...', Object(Mage_Core_Model_Resource_Website))
#16 /var/www/vhosts/mydomain.com/httpdocs/magento/app/code/core/Mage/Core/Model/Abstract.php(213): Mage_Core_Model_Abstract->getResourceCollection()
#17 /var/www/vhosts/mydomain.com/httpdocs/magento/app/code/core/Mage/Core/Model/App.php(608): Mage_Core_Model_Abstract->getCollection()
#18 /var/www/vhosts/mydomain.com/httpdocs/magento/app/code/core/Mage/Core/Model/App.php(466): Mage_Core_Model_App->_initStores()
#19 /var/www/vhosts/mydomain.com/httpdocs/magento/app/code/core/Mage/Core/Model/App.php(349): Mage_Core_Model_App->_initCurrentStore('', 'store')
#20 /var/www/vhosts/mydomain.com/httpdocs/magento/app/Mage.php(684): Mage_Core_Model_App->run(Array)
#21 /var/www/vhosts/mydomain.com/httpdocs/magento/index.php(87): Mage::run('', 'store')
#22 {main}

Error log record number: 764608357299

In fact for some reason it shows "user magento_7@localhost" but this user is the one that was used in the FIRST installation.

I check on phpMyAdmin and that first specific Magento user and his related DB was removed. So how could be possible that? Then I checked that "magento_7" word into my all Magento installation files content and no mention there of it. Just (of course) the new user.

Then I deleted and reinstalled Magento different times with the same "first user" issue (deleted browser cache etc.).

But the interesting things is that I installed Magento on a different domain with different IP and was fine. But when I deleted and installed in the same location again I have the same "first user" (just different because another domain/installation) issue...
So definitely it is a Plesk/Magento problem.