Slackware doesn't install a firewall script by default, but if a file called /etc/rc.d/rc.firewall exists, Slackware will run it at boot after the network is configured. Now that you say that DHCP isn't even working, it's clear that your box isn't talking to the router for whatever reason. Try this. Unplug your router and all other computers. Plug your Linux box straight into the cable modem so that it's talking to your provider. Set it to DHCP and see what happens. If you get an IP address, then we know that the router is the issue. If not, then I'm at a total loss.
