CodingForums.com - i have made my calculator but does not function

could someone let me where i am going wrong?
thank you
Code:
<script language="javascript" type="text/javascript">

<!-- Begin

function Loan() {

var loanAmount;

var IR;

var years;

var monthPay;

var month;

switch(document.calcform.startm.value) {

case "january":

document.calcform.startm.value="0";

parseInt(document.calcform.startm.value)

break;

case "february":

document.calcform.startm.value="1";

parseInt(document.calcform.startm.value)

break;

case "march":

document.calcform.startm.value="2";

parseInt(document.calcform.startm.value);

break;

case "april":

document.calcform.startm.value="3";

parseInt(document.calcform.startm.value);

break;

case "may":

document.calcform.startm.value="4";

parseInt(document.calcform.startm.value);

break;

case "june":

document.calcform.startm.value="5";

parseInt(document.calcform.startm.value);

break;

case "july":

document.calcform.startm.value="6";

parseInt(document.calcform.startm.value);

break;

case "august":

document.calcform.startm.value="7";

parseInt(document.calcform.startm.value);

break;

case "september":

document.calcform.startm.value="8";

parseInt(document.calcform.startm.value);

break;

case "october":

document.calcform.startm.value="9";

parseInt(document.calcform.startm.value);

break;

case "november":

document.calcform.startm.value="10";

parseInt(document.calcform.startm.value);

break;

case "december":

document.calcform.startm.value="11";

parseInt(document.calcform.startm.value);

break;

default:

document.calcform.startm.value="0";

parseInt(document.calcform.startm.value);

break;

}

loanAmount = parseFloat(document.calcform.price.value);

IR = parseFloat(document.calcform.interest.value);

years = parseFloat(document.calcform.time.value);

loanAmount = loanAmount + int;

month = years * 12;

interestRate = IR / 12;

negmonth =- 1 * month;

var bottom = 1 - (Math.pow(interestRate+1,negmonth));

var top = interestRate;

var mid = top / bottom;

var dec;

document.calcform.monthPay.value = (loanAmount * mid);

monthPay = document.calcform.monthPay.value;

document.calcform.monthPay.value = eval(monthPay);

loanAmount = loanAmount - document.calcform.monthPay.value;

document.calcform.month.value = month;

}

function convert() {

var startmonth = new String();

startmonth = document.calcform.startm.value;

document.calcform.startm.value = startmonth.toLowerCase();

}

function changenum() {

document.calcform.startyear.value=parseInt(document.calcform.startyear.value);

}

var d = new Date;

function getFieldValue (strFieldName) {

var strFieldValue;

var objRegExp = new RegExp(strFieldName + "=([^&]+)","gi");

if (objRegExp.test(location.search))

strFieldValue = unescape(RegExp.£1);

else strFieldValue="";

return strFieldValue;

}

function Currency(money1) {

var money = new String(money1);

var decimal = money.indexOf(".",[0]);

var money = money.substring(0,decimal+3);

var money1 = parseFloat(money);

return money;

}

var startmonth;

startmonth = getFieldValue("startm");

var monthofpayment = new String;

month = getFieldValue("month");

monthPay = getFieldValue("monthPay");

loanAmount = getFieldValue("price");

Ir = getFieldValue("interest");

Ir = Ir/12;

year = getFieldValue("startyear")

function check() {

var price = document.calcform.price.value;

if(price.indexOf(",") >= 0) {

alert("Please do not put commas in the Price number")

   }

}

//  End -->

</script>

<center>

<form method="calc.loan">

<table border=0>

<tr>

<td valign="top">

Anticipated Amount of Loan

<br>

</td>

<td valign="top">

£

<input name=price onblur="check()" size=10>

</td>

</tr>

<tr>

</tr>

<tr>

<td>

Anticipated Interest Rate(.00 format)

<br>

</td>

<td>

<input name=interest size=10>

<br>

</td>

<tr>

<td>

Anticipated length of loan, in years.

<br>

</td>

<td>

<input name="time" size=10>

<br>

</tr>

<tr>

<td>

Start Date of Loan (month and year)

</td>

<td>

<input name=startm onblur="convert()" size=10>

<input name=startyear onblur="changenum()" size=10>

</td>

</td>

</tr>

<input name=month type=hidden>

<input name=monthPay type=hidden>

<tr>

<td>

<input type=submit value="Calculate Loan" onmouseover="check()" onclick="Loan()">

</td>

</tr>

</table>

</form>

<table border=0>

<tr>

<td>

Loan Price

</td>

<td>

£

<script language="javascript">

<!--

document.write(getFieldValue("price"));

//-->

</script>

</td>

</tr>

<td>

Monthly Payment

</td>

<td>

£

<script language="javascript">

<!--

var payment = getFieldValue("monthPay");

payment=Currency(payment);

document.write(payment);

//-->

</script>

</td>

</tr>

<tr>

<td>

# of years

</td>

<td>

<script language="javascript">

<!--

document.write(month/12);

-->

</script>

</td>

</tr>

</table>

<table border="1" >

<tr>

<th width="125">

Month/Year

</th>

<th width="125">

Interest

</th>

</tr>

<script language="JavaScript">

<!--

var halfmonth;

halfmonth = month / 2;

for(y = 0; y <= month; y++) {

var interest = loanAmount * Ir;

var principal = monthPay - interest;

loanAmount = loanAmount - principal;

interest = Currency(interest);

principal = Currency(principal);

if(startmonth > 11) {

startmonth = 0;

year++;

}

switch(startmonth.toString()) {

case "0":monthofpayment="January";

break;

case "1":monthofpayment="February";

break;

case "2":monthofpayment="March";

break;

case "3":monthofpayment="April";

break;

case "4":monthofpayment="May";

break;

case "5":monthofpayment="June";

break;

case "6":monthofpayment="July";

break;

case "7":monthofpayment="August";

break;

case "8":monthofpayment="September";

break;

case "9":monthofpayment="October";

break;

case "10":monthofpayment="November";

break;

case "11":monthofpayment="December";

}

document.write("<tr><td width='125'>")

document.write(monthofpayment+" "+year+"</td>"+"<td width='125'>"+"£"+interest+"</td><td width='125'>"+"£"+principal);

document.write("</td></tr>");

startmonth++;

}

//-->

</script>

</table>

</center>