My droplet configuration: Ubuntu 14.04.1 LTS / Apache/2.4.7 (Ubuntu)

My DNS configuration:
*$ORIGIN mercadoallegro.com.br.
$TTL 1800
mercadoallegro.com.br. IN SOA ns1.digitalocean.com. hostmaster.mercadoallegro.com.br. xxxxxxxx
....
www.mercadoallegro.com.br. 1800 IN CNAME mercadoallegro.com.br.
*
In /etc/apache2/sites-available: (two files: )
*default-ssl.conf mercadoallegro.com.conf
*
cat mercadoallegro.com.conf in /etc/apache2/sites-available:

*<VirtualHost *:80>
ServerName mercadoallegro.com.br
ServerAlias www.mercadoallegro.com.br
ServerAdmin me@gmail.com
DocumentRoot /var/www/html
ErrorLog ${APACHELOGDIR}/error.log
CustomLog ${APACHELOGDIR}/access.log combined
</VirtualHost>
*
in /etc/apache2/sites-enabled (three files) :
000-default.conf.old mercadoallegro.com.conf zzz-default.conf.old
(the file mercadoallegro.com.conf has the same content that before presented)

I have registered my domain in registro.br and it's working, in other words, www.mercadoallegro.com is work but my navigator imediatly changes the domain name by ip server.

I had restarted apache2 service a lot of times.

ASK: What I did wrong? And how can I configurate my server, droplet and what else necessary to keep the domain name in navigator ????
ps.: I don' t have cpanel or vestacp , and I am a newbie. Please help me I 'm in a couple of days in this problem and didn't found a tutorial or help .
I followed this tutorial : https://www.digitalocean.com/community/tutorials/how-to-set-up-apache-virtual-hosts-on-ubuntu-12-04-lts but couldn't help me
And others tutorials more.