Quite possibly you will need to look at access log, it could give you some kind of HTTP code.*By the way, if you are running ssl, then you need to look at ssl_error_log, you can specify how the error log is called too, so be sure to check out if you have no other log files available in /var/log/httpd, that is - if you got centos, if not, then the log files might be in different location.