Apt-get/wireshark/synaptic failed

Suddenly, on Hardy beta, I can no longer use apps like wireshark, etherape, synaptic, or apt-get! I recently changed my domain name and changed it back; but after I did that I could not launch synaptic! I can still get on the internet (I'm reporting this bug on the computer in question), and do local networking but when I type: "sudo apt-get update" into a terminal I get: "sudo: unable to resolve host ubuntu-laptop". On the same machine, on Vista, I can use wireshark fine.

What happened and what do I do?