Configuring two networks on a Windows 7 machine may result in a “no network access” error message. First, I assume you have checked to make sure that a networkd interface card driver for a second network card is not having problems in device manager via control panel. If your first network interface card is set to DHCP to connect to your ISP, then your second NIC card is set to static ip address to connect to your internal network.
You can try disconnecting your first network interface card from your ISP, and trying to setup your second network interface card with a static IP address that is on the same subnet as your internal network, for testing purposes. You should be able to at least ping your internal network device(s) by putting that second network interface card on that same subnet as an internal network is setup on.
For example:
LAN NIC card
IP: 192.168.1.1
Subnet Mask: 255.255.255.0
Gateway: blank or 192.168.1.2 (same as your DNS)
Preferred DNS: 192.168.1.2
Your internal network device could have an IP address of 192.168.1.2 on a 255.255.255.0 subnet mask. This is all dependent on if you are using a hub, switch, or router to connect your second network interface card to your external network device(s). Don’t forget to try adding your Windows computer to a same work group or domain that your domain server is on.
A following networking tutorial is for Windows Vista, but I think this may be your answer for two networks on Windows 7.