VPS: Apache port 80 not accessible

I have reinstalled CentOS 5.5 on my un-managed VPS. Everything is fine except port 80

I am trying to access IP address in Internet Explorer but seems port 80 is not accessible.

I have checked by changing Listen 80 to Listen 90 in httpd.conf

and accessed the ipaddress with port 90 i.e. and apache page was displayed

I need help on how to resolve this issue

is it posible something else is blocking port 80?

netstat -pan | grep 80 will show any processes that are listening on port 80.