Mysqli makes use of object oriented programming. Try using this approach instead:
function dbCon() {
if($mysqli = new mysqli('$hostname','$username','$password','$databasename')) return $mysqli; else return false;
}
if(!dbCon())
exit("");
else $con=dbCon();
if (isset($_GET['part'])){
$partid = $_GET['part'];
$sql = "SELECT *
FROM $usertable
WHERE PartNumber = $partid";
$result=$con->query($sql_query);
$row = $result->fetch_assoc();
$partnumber = $partid;
$nsn = $row["NSN"];
$description = $row["Description"];
$quantity = $row["Quantity"];
$condition = $row["Conditio"];
}
Let me know if you have any questions, I could not test this code so you might need to tripple check it!