Interactive WhiteboardsBlank screen on whiteboard

Thanks Nicola, 

Technically you should be getting an image, even if there was no board installed, the projector should just be projecting the image, whether it be on a board or a wall or a screen. 
Do you have a separate VGA cable by any chance?
What I would like you to try, if you do, is to connect a VGA cable directly from the VGA port on your laptop into the back of the projector. You will have to unplug the VGA plug that is currently going in to the back of it and connect the cable instead. 
If that works, then there might be an issue with the wallbox that your current VGA cable is most likely going to from your laptop at the moment.