为什么这段代码没有将数据插入数据库？

This is my registration form I am using both javascript and php for validating form, javascript code works well in showing validation error messages however somethings wrong with php code,when javascript is disabled php code should show form validation error messages by refrshing page on form submit,but no error messages appear and no data is inserted. On clicking submit, page is reloaded but even form does not appear.

<?php
 error_reporting('E_ALL ^ E_NOTICE');
 if(isset($_POST['reg'])){
 $fn = ucfirst($_POST['fname']);
 $ln = ucfirst($_POST['lname']);
 $un = $_POST['username'];
 $em = $_POST['email'];
 $pswd = $_POST['password'];
 $d= date("Y-m-d");
if (strlen($fn) < 2 || strlen($fn) > 15) {
$error =  "First name must be 2 to 15 characters long";
 }
elseif (strlen($ln) < 2 || strlen($ln) > 15) {
$error =  "Last name must be 2 to 15 characters long";
}
elseif($em==""){
$error =  "Email cannot be empty";
}
elseif (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
$er = "Invalid email format";
}
elseif($pswd==""){
$error =  "Fill your password";
}
elseif($pswd!=$pswd2){
$error =  "Password and Confirm password do no match";
}
else{

$pswd = password_hash($pswd, PASSWORD_DEFAULT);
$stmt = $db->prepare("INSERT INTO table1 (username,firstname,lastname,email,password) VALUES (:username,:firstname,:lastname,:email,:password)");  
$stmt->execute(array(':username'=>$un,':firstname'=>$fn,':lastname'=>$ln,':email'=>$em,':password'=>$pswd));
}
if ($stmt->rowCount() == 1) {
 header("Location:login.php");
} 
else {
echo "Error occured please try again.";
}
}
?>

<form action="" method="post">
<input type="text" name="fname" id="fn" placeholder="First Name"/><br />
<input type="text" name="lname" id="ln"  placeholder="Last Name"/><br />
<input type="text" name="username" id="un" placeholder="Username" class="username" /><br />
<input type="email" name="email" id="em" placeholder="Email"/> <br />
<input type="password" name="password" id="pswd" placeholder="Password"/><br />
<input type="password" name="password2" id="pswd2" placeholder="Confirm Password"/><br />
<input type="submit" id="submit" name="reg" value="Create an Account">
<center><div id="er"><?php echo $error ?></div></center>
</form>

You should echo $error not $er

<center><div id="er"><?php echo $error; ?></div></center>

You are doing a mistake:

$stmt->execute(array(':username'=>$un,':firstname'=>$fn,':lastname'=>$ln,':email'=>$em,':password'=>$pswd));

You should use 'username' instead of ':username'. like this:

$stmt->execute(array('username'=>$un,'firstname'=>$fn,'lastname'=>$ln,'email'=>$em,'password'=>$pswd));

There are a few inconsistencies in your code.

At the beginnig you assign $_POST['email'] to $em, but later you validate against a variable named $email, which doesn't exist at this point.

$em = $_POST['email'];
.
.
.
elseif (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
    $er = "Invalid email format"; //should maybe be $error
}

Then there is the password-validation:

elseif($pswd!=$pswd2){
    $error =  "Password and Confirm password do no match";
}

$pswd2 has never been defined in your code.

$stmt ist defined in the else-block of your validation, but you use it for getting the row-count after the validation. So, if any of your if-statements is true, this will cause an error.

It would be better if you change that part of your code to this:

else{
    $pswd = password_hash($pswd, PASSWORD_DEFAULT);
    $stmt = $db->prepare("INSERT INTO table1 (username,firstname,lastname,email,password) VALUES (:username,:firstname,:lastname,:email,:password)");
    $stmt->execute(array(':username'=>$un,':firstname'=>$fn,':lastname'=>$ln,':email'=>$em,':password'=>$pswd));

    if ($stmt->rowCount() == 1) {
        header("Location:login.php");
    }
    else {
        echo "Error occured please try again.";
    }
}

After all it seems like you haven't error reporting activatet.