Go to Start and search on cmd or command. Right click on either cmd or command then select Run as administrator. At the command prompt type regedit. Navigate to the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\ Services\Tcpip\Parameters\IPEnableRouter setting, right click and select Modify. Change 0 to 1 and exit the editor.
http://windows.microsoft.com/en-us/windows7/Back-up-the-registry
When your back at the command prompt type services.msc and navigate to the Routing and Remote Access service. Right click and select Properties. Change to Automatic and click on Start to start the service.