Project Euler Problem 3 - does not actually work

#!/usr/bin/php
<?php

function isPrime($num) {
    if (!is_numeric($num)) {
        exit(1);
    } elseif ($num < 1) {
        exit(2);
    } elseif ($num == 1) {
        return false;
    }

    $half = ceil(($num / 2) + 1);
    for ($x = 2; $x < $half; $x++) {
        if ($num % $x == 0) {
            return false;
        }
    }
    return true;
}

function getFactors($num) {
    if (!is_numeric($num)) {
        exit(3);
    } elseif ($num < 1) {
        exit(4);
    } elseif ($num == 1) {
        return array(1);
    }

    $factors = array();
    echo "number: \t$num\n";
    for ($x = 1; $x <= $num; $x++) {
        if ($num % $x == 0) {
            $factors[] = $x;
            echo "new factor:\t$x\n";
        }
    }
    return $factors;
}
echo("start: " . ($start = time()) . "\n");
$factors = getFactors(600851475143);
echo("end:   " . ($end = time()) . "\n");
echo("total: " . ($end - $start));

echo($start = time() . "\n");
foreach ($factors as $factor) {
    echo $factor . ": \t";
    if (isPrime($factor)) {
        echo "prime\n";
    } else {
        echo "not prime\n";
    }
}
echo($end = time() . "\n");
echo("total: " . ($end - $start));