Can't sign up using my DB - php

Question

I need to make a Sign in form for my website. And I have to use MySQLi because MySQL will cause decaprated on my try.
So, here's the index.php code:
<?php
session_start();ob_start();
$con=mysqli_connect("localhost","root","","oos");
if (mysqli_connect_errno()) echo "Failed to connect to MySQL: " . mysqli_connect_error();
if(isset($_POST['signin']))
{
$username = $_POST['userid'];
$pass = $_POST['password'];
$query1 = "select * from admintb where adID = '$username' and adPass = 'password' ";
$result1 = mysqli_query($con,$query1) or die;
$co=0;
while($row=mysqli_fetch_assoc($result1)) $co++;
if($co==1)
{
$_SESSION['a']=$username;
header("Location: main_menu.php");
}
} ?>
The problem is, when I make $username="admin" and $password = "admin", it will go to main_menu.php alright. But when I try to do as above, base on my database, it won't go to main_menu.php.
How can I sign in, go to the main_menu.php using ID from my database?

Answer 1

Sorry, I already checked it, it's a stupid mistake. Inside this snippet:
$username = $_POST['userid'];
$pass = $_POST['password'];
$query1 = "select * from admintb where adID = '$username' and adPass = 'password' ";
$result1 = mysqli_query($con,$query1) or die;
fix to this:
$query1 = "select * from admintb where adID = '$username' and adPass = '$pass' ";