1. If you are accessing the website by name , make sure it is resolving to an ip address by pinging the address.
2. Check the status of apache is it running ?
3. Check for any syntax error in apache configuration, if it is not running or is being restarted. [ httpd -t ]
2. If the service is failing to start and there is not much information with syntax checker , then check the apache logs at /var/log/httpd/error_log and /var/log/httpd/ssl_error.log
3. Check if the apache is listening on the http or https port , whichever the service is supposed to listen on [ netstat -tupan | grep -i httpd ]
4. Make sure firewall is not running or is configured to allow access to the service ports.
5. Make sure SElinux is turned off or configured to allow httpd to run.