Warning: Cannot modify header information hatası

<?php
ob_start();

include ("Aktarimlar/ayar.php");
include ("fonksiyonlar.php");
Function Anasayfa () {



echo" ÜYE HESABI Burası anasayfa";
}




Function Uye_Kayit (){
tablo_ac();
echo '

<form method="POST" action="index.php?Git=uyehesabi&sayfa=uye_kaydet">
    <div align="center">
    <table border="0" width="85%" cellspacing="0" cellpadding="0">
        <tr>
            <td width="100%" height="1" colspan="3"> </td>
        </tr>
        <tr>
            <td width="22%"> Kullanıcı Adı</td>
            <td width="9%" align="left">:</td>
            <td width="69%" align="left">
            <input type="text" name="kullanici" size="25"> <font color="#FF0000">
            (*)</font></td>
        </tr>
        <tr>
            <td width="22%"> Şifre</td>
            <td width="9%" align="left">:</td>
            <td width="69%" align="left">
            <input type="password" name="sifre" size="25"><font color="#FF0000"> 
            (*)</font></td>
        </tr>
        <tr>
            <td width="22%"> Email</td>
            <td width="9%" align="left">:</td>
            <td width="69%" align="left">
            <input type="text" name="email" size="25"> <font color="#FF0000">(*)</font></td>
        </tr>
        <tr>
            <td width="22%"> Cinsiyet</td>
            <td width="9%" align="left">:</td>
            <td width="69%" align="left">
            <img border="0" src="Resimler/user-bay.gif" width="22" height="22"><input type="radio" value="Bay" checked name="cinsiyet">Bayan 
            <img border="0" src="Resimler/user-bayan.gif" width="22" height="22"><input type="radio" value="bayan" name="cinsiyet"> 
            Bayan</td>
        </tr>
        <tr>
            <td colspan="3">
             </td>
        </tr>
        <tr>
            <td colspan="3">
            <p align="center"><font color="#800000"><b>Kullanıcı Özel Bilgileri</b></font></td>
        </tr>
        <tr>
            <td width="22%"> </td>
            <td width="9%" align="left"> </td>
            <td width="69%" align="left"> </td>
        </tr>
        <tr>
            <td width="22%"> Adı Soyadı</td>
            <td width="9%" align="left">:</td>
            <td width="69%" align="left">
            <input type="text" name="adsoyad" size="43"></td>
        </tr>
        <tr>
            <td width="22%"> Ülke / Şehir</td>
            <td width="9%" align="left">:</td>
            <td width="69%" align="left">
            <input type="text" name="ulke" size="18"> /
            <input type="text" name="sehir" size="19"></td>
        </tr>
        <tr>
            <td width="22%"> İmza</td>
            <td width="9%" align="left">:</td>
            <td width="69%" align="left"><textarea rows="8" name="S1" cols="33"></textarea></td>
        </tr>
        <tr>
            <td width="22%"> </td>
            <td width="9%"> </td>
            <td width="69%"><input type="submit" value="Gönder" name="B1"></td>
        </tr>
        <tr>
            <td width="22%"> </td>
            <td width="9%"> </td>
            <td width="69%"> </td>
        </tr>
        <tr>
            <td width="100%" colspan="3">
            <p align="center"><b>NOT: <font color="#FF0000">(*) </font>
            <font color="#808080"> ile Bilirtilen alanlar doldurulmak 
            zorundadır.</font></b></td>
        </tr>
    </table>
    </div>
</form>


';


tablo_kapat ();
}





Function Uye_Kaydet(){

$kullanici         =Kod_Temizle($_POST["kullanici"])         ;
$sifre            =$_POST["sifre"]              ;
$adsoyad        =Kod_Temizle($_POST["adsoyad"])             ;
$ulke            =Kod_Temizle($_POST["ulke"])             ;
$sehir            =Kod_Temizle($_POST["sehir"])             ;
$email            =Kod_Temizle($_POST["email"])             ;
$cinsiyet        =$_POST["cinsiyet"]                        ;
$imza            =İcerik_Temizle($_POST["imza"])             ;


if(($kullanici=="") or ($sifre=="") or ($email=="")){    

    echo "<script>
    alert(\"Lütfen Boş Alan Bırakmayın\")
    </script>";

    echo "<br><center>Yönlendiriliyorsunuz <BR>Lütfen Bekleyin</center><br>";
    header("Refresh: 2; url=index.php");
    
    }else{
}
}
$sayfa = $_GET["sayfa"];

switch ($sayfa) {



        default                :                     Anasayfa ()            ;             Break     ;
        case ("uye_kaydi")    :                     Uye_Kayit ()        ;            Break    ;
        case ("uye_kaydet")    :                     Uye_Kaydet ()        ;            Break    ;
        
    
}



?>