I had the exact same issue on a win7 pro.
I managed to solve the problem after reading the posts made in this topic. It was making me crazy and I was gonna reinstall windows!
Not sure what the problem is and what causes it but I solved it by replacing the following registry entries. I replaced them with the entries form another working PC
U can do the same or just use the fix.reg file I attached. Just make sure u change "Hostname" and "NV Hostname" entries with ur PC name. U might also want to take a backup of those registry entires.
fix.zip
Here is the regsitry address:
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\Tcpip\Parameters]
Instead of CurrentControlSet u might see ControlSet001 or 002. I replaced those too.
Hope this helps