I've got exactly the same problem as you have. Since 4th of January i am trying to get online with the result of "Server Failed to respond to Login attempt."
Tried everything i could imagine, from reinstalling the client and net7 to compatibilty mode, shutting down firewall , fixed net7, .net3.5 reinstall C++ stuff and so on yet i did't find any way to get online. Close to give up all hope. Yes admin mode aint the issue either