First of what version are you using & what is your config of your system?
Do you have webmin installed on the system?
It can be that your smb setup is on the wrong nic on your box.
on Version 3.2 have a look in /etc/samba/smb.conf you should have something like this
bind interfaces only = yes
interfaces = eth1 eth2
make sure that your internal nic is in that list.
also make sure that your firewall is setup correctly: 1 internal, 1 external.
hope this help.