1. Open the registry with regedit.exe
2. Go to the path: HKLM/System/CurrentControlSet/Services/Tcpip/Parameters/Interfaces/
3. Here you'll need to select the CLSID of your networkadapter where you change the settings. You'll probably recognize it by looking at the value IPAddress that will have the IP of this adapter.
4. Open the value "DefaultGateway" by doubleclicking it. You will see a list of all the gateways that disappeared! (maybe in your case it will be only one, in my case there were due to lots of testing several addresses) Very likely, the first line will be empty. I'm not sure, how this little flaw can make such a big problem. However, if you manually remove this first empty line, click OK and reboot your system everything should be working fine again.
Things worked fine until the last system update which added this old problem this old problem back into the system.