The location of your error logs depends on your OS, webserver software, and versions.
For Apache
consult your httpd.conf or apache2.conf
For PHP
You could create a temp.php and in it put
<?php phpinfo(); ?>
and then browse to it, and it should display a listing of tyour PHP's configuration.
Which includes the error_log location for PHP.
For IIS you would look in your IIS Management panel to see where the logs are and open them.
