为什么我无法访问我的数据库？

This my dbconnect.class.php

<?php 

class Connect
{
    //public $error;
    public $db;
    public function __construct()
    {
        $link = mysql_connect("localhost","root","1");
        $db = mysql_select_db("tarih",$link);
        $this->db = $db;
    }
}

$connect = new Connect();
$connect = $connect->db;
?>

And this is main php file (header.class.php)

<?php
require_once ('dbconnect.class.php');
class Header extends Connect
{ 
    public $headers = array();
    public function __construct() 
    { 
        /* 
        * Bu sınıf sayfaların header bilgilerini işler. 
        */  
    } 

    public function sayfaHeader($sayfa = true) 
    { 
        $sql = "SELECT * FROM header WHERE id='" . $sayfa . "'"; 
        $query = mysql_query($sql,$connect) or mysql_error(); 
        echo $sql;
    } 


} 

$header = new Header();
echo $header->sayfaHeader();
?>

But when i run this code I see this error:

Warning: mysql_query(): supplied argument is not a valid MySQL-Link resource in C:\AppServ\www\ilk\class\header.class.php on line 16

What is the problem?

Your $connect variable is a parent class. You need to point to the $link variable it contains.

Change:

$query = mysql_query($sql, $connect) or mysql_error(); 

to

$query = mysql_query($sql,$link) or mysql_error(); 

The variable $connect is not in the scope of the class. Either you leave it out and mysql_query chooses the last available resource. Or you can pass-through your $connect variable into the class:

require_once ('dbconnect.class.php');
class Header extends Connect
{ 
    public $headers = array();
    protected $database;

    public function __construct($database) 
    { 
        /* 
        * Bu sınıf sayfaların header bilgilerini işler. 
        */  
        $this->database = $database;
    } 

    public function sayfaHeader($sayfa = true) 
    { 
        $sql = "SELECT * FROM header WHERE id='" . $sayfa . "'"; 
        $query = mysql_query($sql,$this->database) or mysql_error(); 
        echo $sql;
    } 
} 

$header = new Header($connect); // here you pass-through your resource
echo $header->sayfaHeader();

I also want to mention that you should look into Design Patterns, because it's just some pseudo OOP which you are creating.