Network no longer sharing

I've been using a home network for file sharing for years now. Last week I moved house, and now my main PC no longer shares.
It's still set up to share the shared folder, but it can't be accessed from any of the other devices on the network. I have a second laptop on the same network and it can be accessed by other devices, except for the main PC.
UPnP is also not detecting either to or from the main one.
I've tried going into the computer properties>computer Name tab to change the network settings but the "Network ID" button is greyed out.

I really don't have a clue what else to do, and its driving me insane because I use this PC to stream media to my xbox. Can anyone give any recommendations.
My PC is running Windows XP MCE2002 SP2. I've also disabled Norton Internet Security to make sure no firewall is doing anything, but I have been sharing with this on for several months so I don't know if that could be it.
Any help/advice is greatly appreciated

Leroux.