validation not validating

[buzzby]

i had this javascript validation working a few days ago. now, it is only part working. one if statement does a check on fields entered like name, email address, postcode etc. the other if statement deals with radio buttons. now the radio button script doesnt work at all. does anyone know how that can be?

if (mainform.contactpostcode.value=='') 
      { 
      alert('Your contact postcode is a required field. Please try again.'); 
      event.returnValue=false; 
      } 
   if (!(mainform.doyouneed[0].checked || mainform.doyouneed[1].checked || mainform.doyouneed[2].checked || mainform.doyouneed[3].checked)) 
      { 
      alert('Your need is a required field. Please try again.'); 
      event.returnValue=false; 
      } 

[buzzby]

this is the whole javascript code

<SCRIPT>
function validate() {
	if (mainform.name.value=='')
		{
		alert('Your name is a required field. Please try again.');
		event.returnValue=false;
		}
	if (mainform.email.value=='')
		{
		alert('Your email is a required field. Please try again.');
		event.returnValue=false;
		}
	if (mainform.contactaddress.value=='')
		{
		alert('Your contact address is a required field. Please try again.');
		event.returnValue=false;
		}
	if (mainform.workhometel.value=='')
		{
		alert('Your work / home telephone number is a required field. Please try again.');
		event.returnValue=false;
		}
	if (mainform.contactpostcode.value=='')
		{
		alert('Your contact postcode is a required field. Please try again.');
		event.returnValue=false;
		}
	if (!(mainform.doyouneed[0].checked || mainform.doyouneed[1].checked || mainform.doyouneed[2].checked || mainform.doyouneed[3].checked))
		{
		alert('Your need is a required field. Please try again.');
		event.returnValue=false;
		}
	if (!(mainform.designstyle[0].checked || mainform.designstyle[1].checked || mainform.designstyle[2].checked || mainform.designstyle[3].checked))
		{
		alert('Your design style is a required field. Please try again.');
		event.returnValue=false;
		}
	if (!(mainform.project[0].checked || mainform.project[1].checked || mainform.project[2].checked || mainform.project[3].checked))
		{
		alert('Your project is a required field. Please try again.');
		event.returnValue=false;
		}
	if (!(mainform.uses[0].checked || mainform.uses[1].checked || mainform.uses[2].checked || mainform.uses[3].checked))
		{
		alert('Your uses is a required field. Please try again.');
		event.returnValue=false;
		}
	if (!(mainform.programtimecompletion[0].checked || mainform.programtimecompletion[1].checked || mainform.programtimecompletion[2].checked || mainform.programtimecompletion[3].checked))
		{
		alert('Your program time completion is a required field. Please try again.');
		event.returnValue=false;
		}
	if (!(mainform.budgetcost[0].checked || mainform.budgetcost[1].checked || mainform.budgetcost[2].checked || mainform.budgetcost[3].checked))
		{
		alert('Your budget cost is a required field. Please try again.');
		event.returnValue=false;
		}
	if (!(mainform.projectdeadline[0].checked || mainform.projectdeadline[1].checked || mainform.projectdeadline[2].checked || mainform.projectdeadline[3].checked))
		{
		alert('Your project deadline is a required field. Please try again.');
		event.returnValue=false;
		}
	if (!(mainform.whybuild[0].checked || mainform.whybuild[1].checked || mainform.whybuild[2].checked || mainform.whybuild[3].checked))
		{
		alert('Your reason to build is a required field. Please try again.');
		event.returnValue=false;
		}
}
</SCRIPT>

<form method="POST" name="mainform" action="getstartedform.php" onsubmit="validate();">

now it doesnt work at all. well the radio button code doesnt work at all