If you've already connected the cable to your laptop and you've selected the correct input, you might need to hold down the windows key and tap the "p" key on your keyboard to duplicate your screen. This will allow your laptop screen to project properly, and allows for the correct display of presenter mode in PowerPoint.

Make sure the document camera is plugged into the cord labeled HDMI OUT and "Doc Camera" is selected as the source.

Right click on the speaker icon to the lower right of your computer screen and select "Playback Settings" (or, if you have Windows 10, select "Sounds" and click the "Playback" tab). Right click each option and select "Test" until you hear the sound coming from the room speakers. Right click the same option once more and choose "Set as Default Device", then "OK". You should now be able to hear the sound coming out of the classroom speakers.

Try turning on the monitor by pressing the power button. If the monitor still won't turn on, double check to make sure there are no loose plugs in the back of the screen.