Connecting Dell Latitude E6230 laptop to Dell Inspiron 2350 Monitor

I just purchased a Dell Inspiron all-in-one computer.  I'd like for my laptop to be able to share the monitor as well.  I've attached the HDMI cable to both the laptop and the all-in-one, but when I try to switch the laptop to "Projector Only" it just goes dark.  It's like the laptop is switching, but the all-in-one isn't, if that makes any sense.  Any ideas?

Thanks!