404 Not Found on Subdomain

Hello guys. I got a problem when I try to setup subdomain on apache2.4.7 , ubuntu 14.04. Here are my steps:

1. In the folder “/etc/apache2/sites-enabled”,

<VirtualHost *:80>
DocumentRoot /home/example.com/www/sub
ServerName sub.example.com
</VirtualHost>

and enable it.

2.Create a DNS rule on CloudFlare. (because I use their public SSL service)

point sub.example.com to 1.2.3.4 (my droplet IP address)

Then, when I type sub.example.com it comes 404 not found:

Not Found The requested URL /cgi-sys/defaultwebpage.cgi was not found on this server.

What should I do? Thx