There many things a user should do when encountering this. Herewith some suggestions:-
1. Check your configuration and environment, to see if there is anything abnormal.
2. Make sure the physical connections are securely made, no loose plug and so on.
3. Check the events, system events and protocol event windows, to see what error and system events are reported by the system.
4. Use the audio monitor and call tracer to track the test, to see what is going on.