When you are presenting, you should always do a tech check before you start. This will ensure that you are ready to go and that you don't have any technical issues during your presentation. Ideally, this happens the day before and on the day of the event. At a minimum, do one on the day of the event.
When you are ready to do the tech check, call the AV team and ask them to walk you through what to check.
Some common things to check are: