I had a similar event 3 months ago , when I was still on a trial basis. That day, we had an electric outage for the entire block. That was at 1:30 PM. Since we had no patients scheduled to be seen that day. We turned all PCs off for protection of our machines and closed the office for the rest of the afternoon. Next morning,
The front desk PC with XP was unable to find or connect to the main PC with windows 7. The electric outage disrupted the network. I had no problem to reestablish the network between the windows 7 machines in the office. I still has problem to connect the machine with XP to connect to AC on the main PC with windows 7. I just learned that windows xp can not connect to windows 7 unless it is set up to workgroup not homegroup network. Based on that information if your other machines are windows XP and the the main PC is windows XP, they all need to be on workgroup network not as homegroup including the windows 7 machine
I hope this help. If you still have problem connecting to the main PC only for AC then it is AC connection problem. This is my problem now. If you find a solution for it let us know.