The internal server error is a generic error that is impossible to troubleshoot due to lack of detail.
try adding the following to the store/install/index.php file at line 1:
<?php
error_reporting(E_ALL);
ini_set('display_errors','on');
?>
this may tell us the real error that is occurring, if not, you will need to contact the host and look in the server error log.
Once we know the real error that is occurring we can start troubleshooting the cause.