When the light on the HDMI board is blinking that means the board is not receiving any signal from the computer (or RaspberryPi).

• Check that the HDMI cable is connected securely
• Check that the PC is showing a second display. If it does not check the cables.
• Check the short HDMI male to female cable inside the D7 has not come loose. You can always try and bypassing this cable by plugging the HDMI from the PC directly into the HDMI driver board.