Yes, I BELIEVE you that both are on the net. But obviously, since you've installed that new connection, something went wrong or is going wrong. That's why I've asked you to try and network the two computers without the internet connection, by using a private IP range.
The target of trying this is to see where the problem actually resides. If you can connect to your Windows machine using a private IP network without an internet connection, then you can safely say that your problem is connected to the PPPoE router or ISP.