If the C7 is down and ater is up it can mean
1) There is BER on the Ater and as the C7 is more sensitive then the ater so the C7 can remain down.
2) Get the Loop Break checked at both BSC and XCDR end to confirm any mismatch at TXN end.
3) There is Mismatch between the CIC on which the C7 is defined between BSC and MSC.
Try : move the C7 on another Ater and check if it comes or not, move the C7 on another CIC if you are sure about the Ater, i have faced similar problems many times in our NW.
Which Vendor equipment are you using