If the lectern microphone still doesn't work, you can probably assume it is bad. If it does work, you have eliminated the lectern microphone as the source of the problem. Taking care of your cables will help keep problems to a minimum. Let's say the lectern microphone worked. Now try the portable cable that was first connected to the lectern microphone.
Cables are always the greatest source of problems in any system.
Again, substitute the suspected cable with a known good cable. Gently move and twist the cable and connectors to make sure you don't have an intermittent connection. Perhaps the problem was a poor connection caused by contact oxidation or some dirt. Just plugging and unplugging can help clean the connector contacts. It could be the microphone jack on the platform.