I use DB version. Tryed to delete the database table poll_user and to recover it with other hash, but doesn't work
You don't delete the table. You edit the table, only deleting the password that is stored inside the table.
Below is code from database version of poll/include/config.inc.php.
$POLLDB["dbName"] = "";
$POLLDB["host"] = "localhost";
$POLLDB["user"] = "root";
$POLLDB["pass"] = "";
$POLLDB["class"] = "class_mysql.php";
As you can see, it has a place for the password. Try checking your include/config.inc.php. Is there a password? is it encrypted?
Whenever I need to get into an admin panel that I don't have the password for but do have access to the files, I just delete the password from the config.inc.php and the password stored in the database table. Since both are now blank, no password is required to access the Admin Panel. Then, once in Admin, I add a new password. However, I am not using the poll database version, so I can't say that will work for sure.