I have 3 Nortel Networks NT8B27JAAA T7316E phones for my office at work. We just moved office buildings and AT&T came to set up our internet and phone lines. The phones were running just fine until they were moved to the new building. All the phones do is flash red on the mute, speaker, and headset buttons. I cannot do anything on them. They were unplugged from the previous office with cords and placed in new office with same cords. AT&T cannot seem to figure out the problem.. anyone able to help me out? Thanks.