I think you are probably running with SELinux enabled. This requires additional steps to make resources accessible (which is good for security).
These questions have guidelines on how to enable your DocumentRoot:
- https://serverfault.com/questions/293866/apache-says-documentroot-doesnt-exist-when-it-does
- https://serverfault.com/questions/323511/selinux-on-rhel6-httpd-config-documentroot-path-does-exist-does-not-exist
If you don't want to work with SELinux, you can disable it by setting SELINUX=disabled
in /etc/selinux/config. The following links might help if you want to learn more.