There was a similar issue posted in
this thread and a followup thread
here. When you look at your httpd.log file, what HTTP status code do you get when trying to access install.php or search.php: 200, 301, 302, 401, 403, 404? Also, if you set
error_reporting(E_ALL); at the top of config.php, does anything print onsceen when trying to access install.php or search.php?