Checkboxes are not be enabled

I added some javascript that worked yesterday but now it is not working. When the oh.value is a certain number checkboxes are checked.

var oat = this.getField("OrderAmtTotals");

var oa3 = this.getField("OrderAmt3");

var oa4 = this.getField("OrderAmt4");

var hr = this.getField("HostRetailTotal");

var oh = this.getField("OrderPlusHostRetail");

if ((oa4.value !=null) || (oa3.value !=null && hr.value !=null))

{

if (oh.value < 150.00)

{

event.value = 0;

getField("HalfPrice1").checkThisBox(0,false);

getField("HalfPrice2").checkThisBox(0,false);

getField("HalfPrice3").checkThisBox(0,false);

getField("HalfPrice4").checkThisBox(0,false);

getField("HalfPrice5").checkThisBox(0,false);

}

else if (oh.value > 149.99 && oh.value < 300)

{

event.value = oh.value * .10;

getField("HalfPrice1").checkThisBox(0,true);

getField("HalfPrice2").checkThisBox(0,true);

getField("HalfPrice3").checkThisBox(0,false);

getField("HalfPrice4").checkThisBox(0,false);

getField("HalfPrice5").checkThisBox(0,false);

}

else if (oh.value > 299.99 && oh.value < 600)

{

event.value = oh.value * .15;

getField("HalfPrice1").checkThisBox(0,true);

getField("HalfPrice2").checkThisBox(0,true);

getField("HalfPrice3").checkThisBox(0,true);

getField("HalfPrice4").checkThisBox(0,false);

getField("HalfPrice5").checkThisBox(0,false);

}

else if (oh.value > 599.99 && oh.value < 1000)

{

event.value = oh.value * .20;

getField("HalfPrice1").checkThisBox(0,true);

getField("HalfPrice2").checkThisBox(0,true);

getField("HalfPrice3").checkThisBox(0,true);

getField("HalfPrice4").checkThisBox(0,true);

getField("HalfPrice5").checkThisBox(0,false);

}

else if (oh.value > 999.99)

{

event.value = oh.value * .25;

getField("HalfPrice1").checkThisBox(0,true);

getField("HalfPrice2").checkThisBox(0,true);

getField("HalfPrice3").checkThisBox(0,true);

getField("HalfPrice4").checkThisBox(0,true);

getField("HalfPrice5").checkThisBox(0,true);

}

else event.value = 0;

getField("HalfPrice1").checkThisBox(0,false);

getField("HalfPrice2").checkThisBox(0,false);

getField("HalfPrice3").checkThisBox(0,false);

getField("HalfPrice4").checkThisBox(0,false);

getField("HalfPrice5").checkThisBox(0,false);

}