There are several possibilities.
- firewall, iptables configuration
- apache listen address / port
More information is needed about your configuration. What distro are you using? Can you connect via 127.0.0.1?
If the issue is with the firewall/iptables, you can add the following lines to /etc/sysconfig/iptables:
-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 443 -j ACCEPT
(Second line is only needed for https)
Make sure this is above any lines that would globally restrict access, like the following:
-A INPUT -j REJECT --reject-with icmp-host-prohibited
Tested on CentOS 6.3
And finally
service iptables restart
