Thx for your help. I did what you said. But it wasn't just about PHP. The backup made some files break as far as I understand.
This is how I solve:
I download q2a script (the latest version) again.
I copied the followings from old version and put them in new version:
define('QA_MYSQL_HOSTNAME', 'localhost');
define('QA_MYSQL_USERNAME', 'username');
define('QA_MYSQL_PASSWORD', 'password');
define('QA_MYSQL_DATABASE', 'database');
define('QA_MYSQL_TABLE_PREFIX', 'qa_');
Now everything is well.