Cables and Connections
The vast majority of problems that occur with HAM radio equipment is due to faulty cables and faulty cable connections. Whenever you encounter any kind of problem with your setup, first make sure that all your cables are plugged in tightly and in the right spots. If the problems persist, start swapping out old cables for newer ones to see if that makes a difference.
Opened Cables
The next thing you should check for are broken or damaged cables. Check to see if any haven't been soldiered correctly or have bare wires exposed. Also use a voltage meter to check for cables that have internal damage. Once you've removed a cable from your HAM radio equipment and plug both ends into a voltage meter, the meter should read zero. If it does not, the wire has internal damage and will have to be replaced.
Controls
Examine your radio control board and its settings. Oftentimes incorrect settings can be the cause of many problems with HAM radio equipment. For example, if you aren't hearing any sound coming from your headphones make sure the gain is not turned all the way down. If it is, this will essentially mute the audio and cause your headphones not to process any information. Also make sure the antenna switch is in the proper position for broadcasting.