5) /var/log/httpd is where the logs about the web server live. If FreePBX is giving you a blank screen, or you're getting some error message from the web server (404, 403, 500, etc) you can check that locations various logs and see if there's a clue.
6) look in the logs. Most logs are kept in /var/log or various subdirectories of /var/log. Check to see if your particular hardware or application has a log in that area and paste the contents if applicable.
Put large logs on pastebin.ca or pastebin.com. You might want to take the time to sanitize them if they have names or numbers you don't want posted on the Internet. If you do sanitize them, please let us know. It is important.