<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Example</title>
<style type="text/css">
#input{display:none;}
</style>
</head>
<body>
<select name="PB2001" onchange="fifeno(this)">
<option value="?">?</option>
<option value="no">no</option>
<option value="(BG) NFF LO">(BG) NFF LO</option>
<option value="(BG) NFF RX">(BG) NFF RX</option>
<option value="(AT) KKO LO">(AT) KKO LO</option>
</select>
<input name="input" id="input" value="Появился">
<script type="text/javascript">
function fifeno(self) {
var input=document.getElementById('input');
if('no'==self.value) {
if(!input.style.display) {
input.style.display='block';
}
} else if('block'==input.style.display) {
input.style.display='';
}
}
</script>
</body>
</html>