I had the simiar issue: where ystem Status Checks shows.:
|✖|Public DNS (nsd4) is not running (port 53).|
I found out that my server has also ipv6 enabled and nsd4 is not bale to run with ipv6.
So I disabled the ipv6 and started the nsd4 without any problem.
sysctl -w net.ipv6.conf.all.disable_ipv6=0
and
sysctl -w net.ipv6.conf.default.disable_ipv6=0
then
service nsd start
service nsd status
See also: