Run the checks in the 'Bad Microphone?' FAQ. Also, make sure your antenna is configured properly and that the SWR is set if applicable. Make sure your mic is compatible for the system, and that all the connectors under the fairing and seat that carry the mic signal are clean and working properly. If your CB was working and just quit, suspect the mic or antenna first. If you can hear the system 'queue' when you try to transmit, but get no voice, it's probably the mic.