Check power light is on top left hand corner of whiteboard.
If power light is on, then there is power getting to the board. If the light is NOT on, then there is no power to the board. Therefore, check that the whiteboard is plugged into the power socket on wall.
Check the whiteboard icon bottom right hand corner of desktop screen. If there is a red cross on this icon, then there is no connection to the board.
Check that the USB cable from the whiteboard (or promethean grey box) is plugged into the computer. If not, plug it in.
This should solve the connection issue automatically.
But if the red cross is still there, then right click on whiteboard icon bottom right hand corner of desktop, and click "configure". Click on the "find" button and see if it connects. If not, click "connect" button.