I am trying to join a new Windows 7 PC to my domain, however the Network ID box and radio button are both grayed out. I have verified Internet connectivity, and the DNS settings on the PC point to the DNS server. There are many other PCs on the domain, and I add new ones quite often. I've never experienced this issue before. Any help would be appreciated, thanks!
Sounds like you have a home version, you need pro or above to join a domain.