I have an HP Pavilion 550-154na desktop connected to my Dell monitor by HDMI cable from the graphics card, it works fine. But I'd like to connect a second monitor (or projector). The graphics card only has one HDMI port, but the back of the machine has two HDMI ports (covered with black caps), which presumably come off the motherboard. I tried plugging my monitor into one of these ports but the screen stayed blank.
What are my options? Is it possible to get output from these ports or do I need to use a splitter or something?