changing ISP has nothing to do with your LAN.....what you need to find on your LAN is to know which machine is your Master Browser.......Master Browser hold the list of you LAN computer and allow s for quick lookup of local computer......select one computer as master browser and fix the registry setting accordingly:
Here is how:
http://www.windowsnetworking.com/kba...erBrowser.html
Also, you can use software like LANHelper to find out which machine is master browser on your LAN (I would suspect that all of them will report as Master Browser and that's the reason none of the work station will allow other to become the list holder or master browser)
http://www.hainsoft.com/en/
Cheers