I have acquired a network admin position and in doing so inherited a starplus DHS phone system. At this point I am not even sure of the model number of the main control box but I do have an SP7420-00 analog adapter connected to it. It has been working fine until today when I lost one of our 5 lines. It Says “line 3 unavailable “ inbound calls will ring but the system will not let you pick that line up. I called the phone service to show that # busy until I can resolve the issues. Any ideas would be helpful.