想做一个不符合条件提交按钮时灰色的按不了!

<!doctype html>
<html lang="en">
 <head>
  <meta charset="UTF-8">
  <meta name="Generator" content="EditPlus">
  <meta name="Author" content="">
  <meta name="Keywords" content="">
  <meta name="Description" content="">
 <script>
     function verifyTel1() {
         var regexp1 = /^[a-z0-9]{3,9}$/;
         var t1 = document.getElementById("t1").value;
         if (!regexp1.test(t1)) {
             document.getElementById("msg").style.display = "inline-block";
             document.getElementById("msg").innerHTML = "用户名是3-9位不得使用_+!@#$等特殊符号";
             document.getElementById("t1").focus();  //让输入框获得焦点
             document.getElementById("t1").select(); //选中输入框的内容
             setDisabled(true)
             return false;
         } else {
             document.getElementById("msg").style.display = "none";
             return true;
         }
     }     function verifyTel2() {
         var regexp2 = /^[a-z0-9]{6,13}$/;
         var t2 = document.getElementById("t2").value;
         if (!regexp2.test(t2)) {
             document.getElementById("msg2").style.display = "inline-block";
             document.getElementById("msg2").innerHTML = "请输入正确的密码！";
             document.getElementById("t2").focus();  //让输入框获得焦点
             document.getElementById("t2").select(); //选中输入框的内容
             setDisabled(true)
             return false;
         } else {
             document.getElementById("msg2").style.display = "none";
             return true;
         }
     }
     function setDisabled(disabled) {
         document.getElementById('btn').disabled = disabled
     }
     //提交表单
     function submitForm(btn) {
         if (verifyTel1() && verifyTel2()) {
             document.getElementById("allow").submit();
         }
     }
     
 </script>
 </head>
 <body>
<form method="post" action="" id="allow">
<div id="form">
    <div class="int">
        <label for="username">账 号：</label>
        <input type="text" id="t1" class="input" onkeydown="setDisabled(false)" />
    </div><div id="msg"></div>
    <div class="int">
        <label for="txtpwd">密 码：</label>
        <input type="password" id="t2" class="input"  onkeydown="setDisabled(false)" />
    </div><div id="msg2"></div>
<br>
<input type="button" value="提交" onclick="submitForm()" id="btn"/>
</form>
 </body>
</html>