Sometimes named.conf gets corrupted on the cPanel server.
You can see that by creating a DNS report with http://massivedns.com and your nameservers records do not have any IP addresses listed.
Here is the way to fix that in the cPanel servers.
First of all, move the corrupted named.conf using the following command
root@cpanelserver[~]# mv /etc/named.conf /etc/named.conf.bak
Now simply execute the cPanel script to rebuild the named.conf
root@cpanelserver[~]# /usr/local/cpanel/scripts/rebuilddnsconfig
And restart the named service:
root@cpanelserver[~]#/etc/init.d/named restart
All should be fine again!