Thanks for posting! From the information given, I am assuming that what you are trying to do is to share the internet connection that you have established on your Windows 7 PC through a USB Modem, with all the other systems that you that are connected through your wireless router (either through the Ethernet ports on the Wireless router or through wifi).
If the above described setup is your desired setup, the first thing you must ensure is that Internet Connection Sharing (ICS) is enabled on the Adapter (USB Modem in the above described setup) that is providing internet to the Windows 7 PC.
To do that on Windows 7.0 -:
Open Network Connections by clicking the ‘Start’ button , clicking ‘Control Panel’, clicking ‘Network and Internet’, clicking ‘Network and Sharing Center’, and then clicking ‘Change Adapter Settings’.
Right-click the connection that you want to share, and then click ‘Properties’. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
Click the ‘Sharing’ tab, and then select the Allow other network users to connect through this computer’s Internet connection check box. Save by clicking on the ‘OK’ button.
Once ICS is enabled on the Internet connection, please make sure you configure the TCP/IP settings on the Ethernet port of the Windows 7 PC (though which the rest of the systems are going to connect) with a static IP address.
Wireless routers are usually capable of connecting to three Local Area Networks through three internal interfaces. Yours should not be any different. The first interface is through the Internet port on the Wireless router. The second interface is a LAN switch ( which is why you have 4 Ethernet ports all of which connect to one single Local Area Network). The third interface is the Wireless interface which provides connectivity to all the devices connected through WiFi.
If you require all the devices connected though WiFi as well as the Ethernet ports of the Wireless Router to share the internet connection on your Windows 7 PC, you should connect the Ethernet port of the Windows 7 PC to the Internet Port on the Wireless Router. In this case, the Ethernet cable should be a crossover cable. Please make sure that the appropriate TCP/IP settings are configured such that the Ethernet port of the Windows 7 PC and the Internet Port of the router are on the same IP subnet. Check that these ports can ping each other.
If a connection is established, all the systems/devices connected through the other two interfaces of the Wireless Router ( Ethernet ports and Wifi) will be able to connect to the Internet through the Windows 7 PC.
If you only require the systems connected through the Ethernet ports of the Wireless router to share the internet connection on the Windows 7 PC, you can connect the Ethernet port of the Windows 7 PC to the Ethernet Port on the Wireless router as you are doing now. Just make sure that the TCP/IP settings on all systems are static with the gateway set as the Ethernet port of the Windows 7 PC with all the systems configured to be in the same IP subnet.
Hope the above information helps you in setting up your home network with internet connectivity successfully.