Avoid Beep sound when enter keypress in a textbox

<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>

        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>

    </div>
    </form>
</body>
</html>

<input type="text" name="TextBox1" value="" onKeyDown="return StopBeepOnEnter(event)" />

<script type="text/javascript">
    function StopBeepOnEnter(event)
    {
    	if (event.keyCode == 13)
    	{
    		// Do Whatever...

    		return false; // This stops the beep
    	}
    }
</script>

<script type="text/javascript">
    $("#<%=TextBox1.ClientID %>").keydown(function(event)
    {
    	if (event.keyCode == 13)
    	{
    		// Do Whatever...

    		return false; // This stops the beep
    	}
    });
</script>

$("input[type=text],input[type=password]").keypress(function(e) {
  if(e.keyCode == 13) {
    $(this).closest("form").trigger("submit");
    e.preventDefault();
  }
});

$("form").submit(function(e) {
  var txt = $("#txtUser");
  if(txt.val().length == 0) {
    alert("Who are you?");
    txt.focus();
    e.preventDefault();
  }
});

<body onkeypress="if(event.keyCode==13)return false;">