I got a new Windows 7 machine, and was using VNC,SSH etc to connect to my Ubuntu machine, and it worked fine previously. Now it doesn't work if I use the machine's hostname or local IP, but if I use the DynDNS name, it works. I can also access it from my Android phone using the local hostname over SSH.

If I try to connect with SSH to the hostname, it says "Host does not exist". VNC says "Failed to get server address". NX says "no address associated with name", and I don't see it in Windows' "Network" folder.

I've rebooted everything. I've turned off Windows firewall. It was working fine a few days ago, but now it's not. How do I figure out what's blocking it?