尝试获取表单按钮以更改数据库中的值

I am currently trying to get a form button to change a MySQL database table field value? Any ideas where I am going wrong with this code?...

HTML button:

<form><form action="admin.php" method="POST">
<strong>ACTIVE MODE -</strong> Main BaseCentre website is online and active. <input type="submit" value="Maintenance Mode" class="btn btn-default" name="updateclose_site">|
</form>

PHP script:

if (isset($_POST['updateclose_site'])){
$sql = mysql_query("UPDATE adminpage SET close_site='1' WHERE setting='main'");

$sql_doublecheck = mysql_query("SELECT * FROM adminpage WHERE setting='main' AND close_site='1'");
$doublecheck = mysql_num_rows($sql_doublecheck);

if($doublecheck == 0){
echo "<strong><font color=red>> Close site is off</font></strong>";
} elseif ($doublecheck > 0) {
echo "<strong><font color=green>> Close site is working</strong></font><br />";

}
}

My database looks like this:

"headers" setting | close_site (enum, 0, 1, 2, 3)
"rows" main | 0 (default)

Nothing happens when I click the button? Will appreciate any help!

Change html to

<form action="admin.php" method="POST">
<strong>ACTIVE MODE -</strong> Main BaseCentre website is online and active. <input type="submit" value="Maintenance Mode" class="btn btn-default" name="updateclose_site">|
</form>

You have an extra <form>

Another thing. Don't use mysql_ rather use mysqli_ (or PDO) extension
mysql_ is deprecated from php 5.5