I have two computers connected to a router, connected to my ADSL modem by PPPoE. One of those computrs use Windows XP, the other uses Windows 7. The computer using Windows 7 keeps getting limited or no connectivity, and I can't use it to connect to the internet. Connecting the computer to the modem without the router 'in the way' worked, and I was able to use the internet - which led me to believe that the problem is with my router. However, I have changed my router, and the problem persists.

(Just to be clear: the computer using Windows XP can connect to the internet without any problem). This entire question is about the PC using Windows 7.

The only symptom of this problem is that when I see my network devices, in addition to my router (which appears as "Network 4", or something of the sort), I also see an "Unidentified Network". When using ipconfig to check the problem, I see a second gateway, with the IP 0.0.0.0, in addition to the IP of my router.