MySQL - problema al enviar formulario a base de datos

<?php

// datos para la conexion a mysql 

define('DB_SERVER','localhost');

define('DB_NAME','revista');

define('DB_USER','root');

define('DB_PASS','');

$con = mysql_connect(DB_SERVER,DB_USER,DB_PASS) or die (mysql_error($con));

mysql_select_db(DB_NAME,$con) or die (mysql_error($con));

?>

<?php

session_start();

include_once "conexion.php";

if(isset($_POST['enviar']))

{

    if($_POST['nombre'] == '' or $_POST['ape'] == '' or $_POST['correo'] == '' or $_POST['pass'] == '' or $_POST['repass'] == '' or $_POST['date'] == '' or $_POST['sexo'] == '' or $_POST['textarea'] == '')

    {

        echo 'Por favor llene todos los campos.' or die (mysql_error($con));

    }

    else

    {

        $sql = 'SELECT * FROM usuarios';

        $rec = mysql_query($sql);

        $verificar_usuario = 0;

        while($result = mysql_fetch_object($rec))

        {

            if($result->usuario == $_POST['usuario'])

            {

                $verificar_usuario = 1 or die (mysql_error($con));

            }

        }

        if($verificar_usuario == 0)

        {

            if($_POST['pass'] == $_POST['repass'])

            {

                $correo = $_POST['correo'];

                $password = $_POST['pass'];

		$nombre = $_POST['nombre'];

                $apellido = $_POST['ape'];

		$fecha = $_POST['date'];

                $sexo = $_POST['sexo'];

		$direc = $_POST['textarea'];

		$news = $_POST['news'];

		$info = $_POST['info'];

                $sql = "INSERT INTO usuarios (correo,contrasena,nombre,apellido,fechanac,sexo,direccion,temas,news) VALUES ('$correo','$password','$nombre','$apellido','$fecha','$sexo','$direc','$news','$info')" or die (mysql_error($con));

                mysql_query($sql)  or die (mysql_error($con));

                echo 'Usted se ha registrado correctamente.';

            }

            else

            {

                echo 'Las claves no son iguales, intente nuevamente.';

            }

        }

        else

        {

            echo 'Este usuario ya ha sido registrado anteriormente.';

        }

    }

}

?>

<h1>Registro</h1>

    	<form id="sign" name="sign" method="post" action="index.php">

         <label id="registrof"></label><br />

         <label for="nombre">Nombre</label>

         <input type="text" id="nombre" name="nombre" size="18" maxlength="40" onblur="check()" /><label class="check" id="chknombre">

		 </label><br />

         <label for="ape">Apellido</label>

         <input type="text" id="ape" name="ape" size="18" maxlength="40" onblur="check1()" /><label class="check" id="chkape">

         </label><br />

         <label for="correo">Correo</label>

         <input type="text" id="correo" name="correo" size="18" maxlength="40" onblur="check2()" /><label class="check" id="chkcorreo">

         </label><br />

         <label for="pass">Contraseña</label>

         <input type="password" id="pass" name="pass" size="18" maxlength="40" onblur="check3()" /><label class="check" id="chkpass">

         </label><br />

	<label for="pass">Repetir Contraseña</label>

         <input type="password" id="repass" name="repass" size="18" maxlength="40" onblur="checkrepass()" /><label class="check" id="chkrepass">

         </label><br /><br />

         <label>Fecha de Nacimiento</label><br />

         <label>Dia:</label>

         <select id="day" onblur="check4()" name="date" >

         	<option selected="selected" value="">Dia:</option>

            <option value="1">1</option>

            <option value="2">2</option>

            <option value="3">3</option>

            <option value="4">4</option>

            <option value="5">5</option>

            <option value="6">6</option>

            <option value="7">7</option>

            <option value="8">8</option>

            <option value="9">9</option>

            <option value="10">10</option>

            <option value="11">11</option>

            <option value="12">12</option>

            <option value="13">13</option>

            <option value="14">14</option>

            <option value="15">15</option>

            <option value="16">16</option>

            <option value="17">17</option>

            <option value="18">18</option>

            <option value="19">19</option>

            <option value="20">20</option>

            <option value="21">21</option>

            <option value="22">22</option>

            <option value="23">23</option>

            <option value="24">24</option>

            <option value="25">25</option>

            <option value="26">26</option>

            <option value="27">27</option>

            <option value="28">28</option>

            <option value="29">29</option>

            <option value="30">30</option>

            <option value="31">31</option>

        </select>

        <label>Mes:</label>

         <select id="month" onblur="check4()" name="date">

         	<option selected="selected" value="">Mes:</option>

            <option value="Enero">Enero</option>

            <option value="Febrero">Febrero</option>

            <option value="Marzo">Marzo</option>

            <option value="Abril">Abril</option>

            <option value="Mayo">Mayo</option>

            <option value="Junio">Junio</option>

            <option value="Julio">Julio</option>

            <option value="Agosto">Agosto</option>

            <option value="Septiembre">Septiembre</option>

            <option value="Octubre">Octubre</option>

            <option value="Noviembre">Noviembre</option>

            <option value="Diciembre">Diciembre</option>

        </select>

        <label>Año:</label>

         <select id="year" onblur="check4()" name="date">

         	<option selected="selected" value="">Año:</option>

            <option value="2005">2005</option>

            <option value="2004">2004</option>

            <option value="2003">2003</option>

            <option value="2002">2002</option>

            <option value="2001">2001</option>

            <option value="2000">2000</option>

            <option value="1999">1999</option>

            <option value="1998">1998</option>

            <option value="1997">1997</option>

            <option value="1996">1996</option>

            <option value="1995">1995</option>

            <option value="1994">1994</option>

            <option value="1993">1993</option>

            <option value="1992">1992</option>

            <option value="1991">1991</option>

            <option value="1990">1990</option>

            <option value="1989">1989</option>

            <option value="1988">1988</option>

            <option value="1987">1987</option>

            <option value="1986">1986</option>

            <option value="1985">1985</option>

            <option value="1984">1984</option>

            <option value="1983">1983</option>

            <option value="1982">1982</option>

            <option value="1981">1981</option>

            <option value="1980">1980</option>

            <option value="1979">1979</option>

            <option value="1978">1978</option>

            <option value="1977">1977</option>

            <option value="1976">1976</option>

            <option value="1975">1975</option>

        </select><label class="check" id="chkbirth"></label><br /><br />

        <label>Sexo:</label><br />

        <label for="mas">Masculino</label>

        <input type="radio" id="mas" name="sexo" value="Masculino" onselect="check5()"/><br />

        <label for="fem">Femenino</label>

        <input type="radio" id="fem" name="sexo" value="Femenino" onselect="check5()"/><label class="check" id="chksexo"></label><br /><br />

        <label>Indique los temas de los que quiere ser informado:(*)</label><br />

          <label for="news">Noticias</label>

          <input type="checkbox" value="news" id="news" name="news" />

          <label for="new">Nuevos Lanzamientos</label>

          <input type="checkbox" value="new" id="new" name="news" />

          <label for="F1">Formula 1</label>

          <input type="checkbox" value="F1" id="F1" name="news" /><br />

          <label for="rustic">Rusticos</label>

          <input type="checkbox" value="rustic" id="rustic" name="news" />

          <label for="sport">Deportivos</label>

          <input type="checkbox" value="sport" id="sport" name="news" />

          <label for="lux">Lujosos</label>

          <input type="checkbox" value="lux" id="lux" name="news" /><br />

        <div id="signr">

         <label>Direccion donde vive:</label><br />

         <textarea cols="35" rows="10" id="textarea" onkeypress="return checkta(this,100)" name="textarea"></textarea><br /><label class="check" id="chktxta"></label><br />

         </div>

         <div id="final">

          <label for="info">Le Gustaria recibir nuestra informacion en su correo?</label>

          <input type="checkbox" value="si" id="info" name="info" /><br />

          <label>Opcional(*)</label><br /><br />

          <label id="verif">Casilla de Verificacion</label>

          <ul id="validacion">

          <li><label id="num1"></label></li>

          <li><label id="operacion"></label></li>

          <li><label id="num2"></label></li>

          <li>=</li>

          <li><input type="text" id="resultado" maxlength="10" /></li>

          </ul><br />

         <button type="button" id="enviar" onclick="validar()">Enviar</button>

         <input type="reset" id="reset" name="reset" value="Reiniciar" onclick="producto()" />

    	</div>

    	</form>

if(isset($_POST['enviar']))

<button type="button" id="enviar" onclick="validar()">Enviar</button>

<input type="submit" id="enviar" name="enviar">Enviar</button>