Coax outlet does not work

There are four bedrooms (say 1, 2, 3, and 4) in my house and each bedroom has one COAX outlet. Only the outlet in bedroom 1 works. However, I want to install my modem in bedroom 4. How much does it cost to make the COAX outlet in bedroom 4 work? Can COX help to resolve this issue or should I try to find a contractor? Thanks.