I am trying to add demo files from backup file as you describe to manual (step 2) but it stop to respond... after this i cannot open the website

  Thanks for your immediate response!!!!!

Please this... When i am type greek characters and i save the page ... i take this ????????

OK!! I solve the problem by  changing the wordpress wp-config.php file from :
define('DB_CHARSET', 'utf8'); 
to
//define('DB_CHARSET', 'utf8');