Configuring two seperate networks on a Microsoft Windows seven operating system machine may result in a no network access error message. First, I assume you have checked to make sure that a network interface card driver for a second network card is not having problems in Microsoft Windows operating system Device Manager accessible through Control Panel. If your first network interface card is set to dynamic host configuration protocol in order to connect to your Internet service providor, then your second network interface card is configured to use a static Internet protocol address in order to connect to your internal network.
You can try disconnecting your first network interface card from your Internet service providor, and then trying to configure your second network interface card with a static Internet protocol address that is on the same sub network 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 sub network as that internal network is configured as.
For example:
Local area network, network interface card
Internet protocol address: 192.168.1.1
Subnetwork mask: 255.255.255.0
Gateway router: blank or 192.168.1.2, same as your domain name system server address
Preferred domain name system server: 192.168.1.2
Your internal network device could have an Internet protocol address of 192.168.1.2 on a 255.255.255.0 subnetwork 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). You will want to not forget to try adding your Microsoft Windows operating system based computer to that same work group or domain that your domain server is located on.
The following networking tutorial was written for Microsoft Windows Vista operating system. However I think this may be suitable to answer your question on how to configure two networks on Microsoft Windows seven operating system. You can follow this tutorial in order to configure Multiple Networks on Microsoft Windows seven operating system.