The connections on the dock have likely gone bad. Get a replacement dock and you should be all set: http://www.tss-radio.com/t/sirius-car-cradles/

Check the antenna's connector for your car based antenna. Sometimes the little finger tabs need to be gently pushed back towards the center to make a better connection. Be careful not to move them more than a precision screwdrive blade's width or you might snap it off.