为什么程序运行后文件无法上载？

<?php
     if(!$uploadAction):
?><html>
<head>
<title>wen jian shang zai jie mian</title>
</head>
<body><table><center>
<form enctype="multipart/form-data"name="submitform"action="" method="post">
  <input type="hidden" name="uploadaction" value="1">
  <input type="hidden" name="max_file_size" value="10000000">
  <tr>
    <td><input name="uploadfile" type="file" size="30"></td>
  </tr>
  <tr>
     <td><input name="submit" value="提交" type="submit"></td>
     <td><input name="reset" value="重指" type="reset"></td>
  </tr>
</form></center></table></body>
</html><?php
  else:
?><html>
<head>
<title>wen jian shang zai dai ma</title>
</head><?php
  $uploadaction=0;
  $timelimit=60;
  set_time_limit($timelimit);
  $uploaddir='c:/upload';
  $uploadfile=$uploaddir.$_files['usefile']['name'];
  $timefile=$_files['userfile']['tmp_name'];
  $file_size=$_files['userfile']['size'];
  $errno=$_files['userfile']['error'];
   
   if(($tmpfile!="none")&&($tmpfile!=""))
   {
      if($file_size<1024)
   {
  $strfilesize=(string)$file_size."字节";
  }
  else if($file_size<(1024*1024))
   {
  $strfilesize=number_format((double)($file_size/1024),1)."kb";
  }
  else
 {
  $strfilesize=number_format((double)($file_size/(1024*1024))."mb";
  }
 
  if(!file_exist($uploadfile))
   {
           if(move_uploaded_file($tmpfile,$uploadfile))
   {
   echo"文件 $uploadfile($strfilesize)上载成功";
   }
   else
   {
    echo"文件 $uploadfile 失败1 (错误好 :$errno)";
   }
  }
  else
   {
  echo"文件 $uploadfile 已经存在！ （错误好：$errno  ）";
  }
   }
   else
   {
   echo"没选择文件，或则超过了$max_file_size!";
   }
   set_time_limit(30);
?> <br><a herf="nana2.php">返回</a>
 </body>
</html><?
  endif;
?>