hi,many small mistakes you did
always put semicolon when a sentence is complete.
and when adding integer use parseInt function
<script language="javascript" type="text/javascript">
function my()
{
var obj = document.getElementById("t");
var n = obj.getElementsByTagName("input");
var total = 0;
for (var i = 0; i < n.length; i++)
{
if (n[i].checked)
{
var amt = parseInt(n[i+1].value, 0);
if(!isNaN(amt))
{
total += amt;
}
}
}
if ( total > 0)
alert(total);
}
</script>
Happy Coding!
:)