I have an HP 2311x as well. I'm using an HDMI cable and am not having any issues getting the screen to display. I know you said the cable works with a PC but have you tried a different HDMI cable just in case. It might be worth a try. Other than that, I'm not much help.
The issue I had when plugging this monitor into my MBP retina was that the image was very blurry on the HP 2311x. I almost gave up on using it and was going to just buy a Thunderbolt display but after much research I found a custom firmware update that fixed the underscan/blurriness issue. So be prepared for that if you get the screen to display.
If I can find that resource, I will post it here.