Wazz : Antivirus. Just re-joining it to the domain fixed it, but we want to know what caused it in the first place.

oofki : AD won't add the computer unless a domain admin does it. Netbios has nothing to do with it (as far as I know). None of our systems have software firewalls enabled, and no one outside of our IT department can change the name of the computer (plus, it hasn't been changed since it's been moved into this building)