I uploaded the files into my hosting server and im getting this error when i want to open my site what is the problem ? Im using index.php but i think that should not be the problem ?

A 500 is a fairly generic error. If you are trying to access your site and you get this error, you have some code that is crashing the site. it could be in index.php, or another php related file.

is there any difference in file.inc.php and file.php ? i though its because that but its not i have changed the files but not helping..

How do i know where is my error and how do i fix it ? :/
My index.php file is simple with redirecting code

<?php
    require 'connect.php';
    require 'core.php';

    if(loggedin()) {
        header('Location: home.php');
    } else {
        header('Location: login.php');
    }
?>

Check if .htaccess is written well for online environment.

If you ask that. you probably didn't set anything about it.
But just in case see your localhost file how is set and post the code here.
.htaccess file is usually in root directory. But also more files with that name can be found in subdirs as well.

I solved it with reseting the account settings, that helped.