If statement is not working correctly - php

Question

This is my first topic so far in this great webpage
The problem is this:
I'm scripting an UCP (PHP & MySQL based). I want it to show the user's status like score, money, etc. (Yeah, it's for a game) but when I click on the login button nothing happens it just erases the content of the requested fields.
It was working properly before I made some changes (Checking if the username exists)
Here's the code:
if (isset($_POST['login']))
{
$hashedpass = hash('whirlpool', $password);
$query = "SELECT * FROM users WHERE Username = '$playername' AND Password = '$hashedpass'";
$result = mysql_query($query);
$num = mysql_num_rows($result);
mysql_close();
if($num != 0)
{
echo"Account doesn't exist!";
header("Location: ucp.html");
}
else
{
$name=mysql_result($result,$i,"UserName");
$money=mysql_result($result,$i,"Money");
$score=mysql_result($result,$i,"Score");
$wantedlevel=mysql_result($result,$i,"WantedLevel");
$adminlevel=mysql_result($result,$i,"AdminLevel");
echo "<b>$name</b><br>Money: $money<br>Score: $score<br>Wanted Level: $wantedlevel<br>Admin Level: $adminlevel<br><br>";
}
}
else if (isset($_POST['register']))
{
header("Location: register.html");
}
else
{
header("Location: index.html");
}

Answer 1

if($num != 0)
change to:
if($num == 0)

Answer 2

This simply won't work here nor does it make much logical sense:
$num = mysql_num_rows($result);
mysql_close();
if($num != 0)
{
echo"Account doesn't exist!";
header("Location: ucp.html");
}
First the logic is wrong, if $num is NOT equal to 0 then your query MUST have found at least one account. So you need to change your if statement to:
if($num == 0){ //if 0 rows were found - the account was not found thus it doesn't exist
echo "Account doesn't exist!";
}
Notice also i did not add header("location: ucp.html");. You cannot display output + relocate the user to another page. You either do one or the other, or you will get an error/warning.
Finally check your MYSQL is not causing an error by adding a check at the end with :
$result = mysql_query($query) or die(mysql_error());
Final tip, you should avoid using mysql_* and look into mysqli_* or PDO best explained here:
Why shouldn't I use mysql_* functions in PHP?