It is possible you have to change the input from DVI to HDMI in the monitor settings (on the monitor, not from Windows).
That said, you will want to use a dual link DVI-D cable with that monitor. HDMI is not capable of giving you 120hz on that monitor or any other currently being made that I'm aware of. HDMI limits you to 60hz at 1080p. The only advantage to HDMI is it delivers sound and video, if the monitor has speakers on it.