In order to run more than 2 displays on an AMD card, any display after the first two must have DisplayPort output. You cannot use 2 DVI and HDMI, you can only use either 2 DVI, or 1 DVI and 1 HDMI. If your third display does not have DisplayPort, you will have to get an adapter for the third monitor. Check the ports on the back of your card. You may have regular sized DisplayPort, or MiniDisplayPort, and will have to get the appropriate adapter accordingly.