External Monitor Resolution Question

I just bought a rMBP and I wanted to hook it up to my external monitor to work with at home. Much to my dismay, however, when I did so, I could not see the menus and only just the top of the dock. I have an HP monitor (2710 I think) that used 1920x1080 resolution with my Mac mini using an HDMI cable. The computer is smart enough to know that I had an HP 2710 and gives me the choice between the resolution of the internal screen or the HP monitor, although the latter doesn't work. What can I do to fix this problem?