Javascript isn't being called by submit button in HTML - php

Question

For some reason my javascript won't execute when my submit button is pressed. It's supposed to leave an error message beside two textfields for a user's name and email address if they are empty, but it's not and I can't figure out why. Normally, when the two boxes are filled, the submit would go to a php page which sends an email. Any suggestions or help with fixing my javascript problem will be greatly appreciated.
This is my javascript:
//my javascript function
<script type='text/javascript'>
function validate_form()
{
$('span.error_message').html('');
var success = true;
$("#validate_form input").each(function()
{
if($(this).val()=="")
{
$(this).next().html("* You must complete this field"); // the error message
success = false;
}
});
return success;
}
</script>
and my form in html:
<form action=".....whatever....." method="POST" id="validate_form" onsubmit="return validate_form();">
<ol>
<li>
<span id="question">___ is your name? My name is Marie.</span>
<input type="text" name="q1" id="q1" />
</li>
<li>
<span id="question">___ are you from? I'm from Paris, France.</span>
<input type="text" name="q2" id="q2" />
</li>
<li>
<span id="question">Dave: ___ you like football</span>
<p>
<input type="radio" name="q6" value="1" id="q6_1" />
<label for="q6_1">Are</label>
<input type="radio" name="q6" value="2" id="q6_2" />
<label for="q6_2">Do</label>
<input type="radio" name="q6" value="3" id="q6_3" />
<label for="q6_3">Does</label>
<input type="radio" name="q6" value="4" id="q6_4" />
<label for="q6_4">Is</label>
</p>
</li>
<div id="username">
<p>
Before we begin, please enter your name and email:
<br />
<label for="user_name">Name: </label><input type="text" name="user_name" id="user_name" />
<span class="error_message" style="color:#FF0000"></span>
<br />
<label for="user_email">Email: </label><input type="text" name="user_email" id="user_email" />
<span class="error_message" style="color:#FF0000"></span>
</p>
</div>
<p style="width: 242px; margin: auto;">
<input type="submit" name="submit" value="Submit your answers" id="but" />
</p>
</form>
Edit: Fixed the problem with the javascript being called, but now the submit button isn't working even with the two textfields being filled.

Answer 1

$("#validate_form input") - I don't see validate_form anywhere; you need to add it or just use: $("input")

Answer 2

Firebug for firefox would help you debug these types of jscript issues. You can also use the Error Console in Firefox if you dont want to install firebug.