Installing and upgrading help

I'm confused why you didn't use the installation instructions in docs.moodle.org and/or download Moodle from the moodle.org download pages?

There's various things that could cause that error. The quick way to track it down would be to try to access moodle, get the error then do...

$ tail /var/log/httpd/error_log

(I think that's where the apache error log is in Centos)

The log info generated will tell you what went wrong. Chances are it's the file permissions are wrong. Also, looking at those instructions, if you edited the Apache conf file and the web server was *already* started you would need to do a restart on it to make the changes "live"