It might be some other process listening on port 80, which is the well-known port used for HTTP.
If acid_kewpie's methods don't work, try "lsof -i tcp:80" - you may need to install the lsof package.
With RedHat 7.3, that'll be on the disks somewhere, or else you can install APT from
http://freshrpms.net/ and do "apt-get update ; apt-get install lsof".