Tengo este formulario, pero al darle a enviar no pasa nada. No sé donde está el problema
Código PHP:
   <?php 
            ob_start();
            $self = htmlentities($_SERVER['PHP_SELF']); 
        ?> 
        
        <?php
            /*Filtering data*/
            $clean = array();
            $input_errors = array();
            /*control state and collect data*/
            $form_is_submitted = false;
            $input_errors_detected = false;
            $reg_status = false;
        
            if (!empty($_POST['register'])) {
                $form_is_submitted = true;
                $makeHtml = trim($_POST['fullname']);
            /*validate data*/
            if(!empty($_POST['fullname'])) {
                if (strlen($makeHtml)<=100 ) {
                $clean['fullname'] = htmlentities($makeHtml);
                }
            else {
                $input_errors['fullname'] = 'Enter your name, no longer than 100 characters';
                $input_errors_detected = true;
            }
            }
            else {
                $input_errors['fullname'] = 'Please enter your name.';
                $input_errors_detected = true;
            }
            
            $makeHtml = trim($_POST['email']);
                if(!empty($_POST['email'])) {
                    if (filter_var($makeHtml,FILTER_VALIDATE_EMAIL)) {
                    $clean['email'] = htmlentities($makeHtml);
                    }
                else {
                    $input_errors['email'] = 'Please enter a correct email address.';
                    $input_errors_detected = true;
                }
                }            
                else {
                    $input_errors['email'] = 'Please enter your email.';
                    $input_errors_detected = true;
                }
            
            $makeHtml = trim($_POST['user']);
                if(!empty($_POST['user'])) {
                    if (strlen($makeHtml)<=30) {
                        $clean['user'] = htmlentities($makeHtml);
                    }
                    else {
                        $input_errors['user'] = 'Please enter a username, no longer than 30 characters.';
                        $input_errors_detected = true;
                    }
                }    
                else {
                    $input_errors['user'] = 'Please enter your username.';
                    $input_errors_detected = true;
                }
                
            $makeHtml = $_POST['password'];
                if(!empty($_POST['password'])) {
                    if (strlen($makeHtml)<=150) {
                    $clean['password'] = htmlentities($makeHtml);
                    }
                else {
                    $input_errors['password'] = 'Please enter your password';
                    $input_errors_detected = true;
                }
                }
                else {
                    $input_errors['password'] = 'Please enter your password.';
                    $input_errors_detected = true;
                }                
        
            }
        ?>
        
        <!-- Form -->
        
        <form action="<?php echo $self; ?>" method="post">
            <fieldset>
                <?php
                //Correcting errors
                if ($form_is_submitted === true && $input_errors_detected !== false) {
                    echo '<p>Please correct the errors</p>';
                        foreach ($input_errors as $error) {
                        echo '<p>'.$error.'</p>';
                        }      
                } elseif ($form_is_submitted === true && $input_errors_detected === false) {
                // Process data
                $user = array();
                $processing_errors = array();
                $processing_errors_detected = false;
                $username = $clean['user'];
                $email = $clean['email'];
                $handle = fopen('process.php', 'r');
                while(!feof($handle)) {
                    $line[] = fgets($handle);
                    foreach($line as $details_string) {
                        $user_details_all[] = unserialize($details_string);
                    }
                foreach($user_details_all as $user) {
                    if($username == $user['user']) {
                        $processing_errors_detected = true;
                        $processing_errors['user_repeat'] = 'Sorry, this name is already taken. Please insert a new one';
                        break;
                    }
                }
                foreach($user_details_all as $user) {
                    if($email == $user['email']) {
                        $processing_errors_detected = true;
                        $processing_errors['email_repeat'] = 'Sorry, that email is already taken. Please insert a new one';
                        break;
                    }
                }
                }
                fclose($handle);
                    if ($form_is_submitted === true && $processing_errors_detected !== false) {
                        echo '<p>There are errors</p>';
                        foreach ($processing_errors as $error) {
                        echo '<p>'.$error.'</p>';
                        }
                    } elseif ($form_is_submitted === true && $processing_errors_detected === false) {
                        $user = $clean;
                        $details_string = serialize($user).PHP_EOL;
                        $result = file_put_contents('process.php', $details_string, FILE_APPEND);
                    if ($result === false) {
                        echo 'There is an error , please try again.';
                    } else {
                    foreach ($clean as $key => $details) {
                    $_SESSION[$key] = $details;
                    }
                $reg_status = true;
                header('Location: http://titan.dcs.bbk.ac.uk/~lvazqu01/p1fma/index.php?'.SID.'');
                    }
                    }
                }       
                ?>    
 
        <?php 
            if (!empty($clean['fullname'])) {
                $name = htmlentities($clean['fullname']); 
            } else { 
                $name = ''; 
            } 
            if (!empty($clean['email'])) {
                $email = htmlentities($clean['email']); 
            } else { 
                $email = ''; 
            } 
            if (!empty($clean['usern'])) {
                $username = htmlentities($clean['user']); 
            } else { 
                $username = ''; 
            } 
        ?>                 
            <div>
                <label for="name">Full name:</label>
                <input type="text" name="fullname" id="name"/>
            </div>
            
            <div>
                <label for="mail">Email address</label>
                <input type="text" name="email" id="mail"/>
            </div>
            
            <div>
                <label for="username">Username</label>
                <input type="text" name="user" id="username"/>
            </div>
            
            <div>
                <label for="pass">Password:</label>
                <input type="password" name="password" id="pass"/>
            </div>
            
            <input type="submit"
                   name="contactsubmit"
                   value="register" />
            </fieldset>
            
 
        </form>   
 

