Ask the following questions:
Is there any signal on the local monitor or the projector?
What input are you using? Local PC (supplied in classroom), Laptop, or DVD player?
If using a laptop, what type of laptop connection? VGA? HDMI?
Using the Extron/Crestron control panel (could be push button or touch screen on the podium) confirm the projector button is turned ON.
Confirm that the correct input is selected on the control panel.
Confirm that the device connected is turned ON (PC, laptop or DVD player).