Cisco Telecommunications Support

We are having an issue with our phone system. Last week we had a power outage and ever since have only had 2 lines working. Once 2 of us are on the phone, other incoming calls get a busy signal. We have three or 4 lines all coming into our phone system so for some reason some of these lines are no longer being utilized. We want someone to help us fix this issue so that when more than two of our sales reps are on the phone other callers are not getting a busy single and the calls go through to our other phones. We have 4 phones. Two phones are line "201", one is "204" and one is line "207". Calls ring through to 204 than 201 (which has one phone in our lower office and one in the upper office) and finally 207 rings last.