Cannot get 4th monitor working

Hello everyone! I'm having some issues getting a 4th display working with my system. I have 3 32" samsung displays in a 3x1 setup and I want to add an additional 24 inch dell monitor off to the side. When I try to enable the display in windows screen resolution settings it will not let me save the settings giving me an error "unable to save display settings". 

I have a Radeon 7990 with 4 HDMI to mini displayport connections that work with the samsung tv's but not the dell monitor. I've also tried connecting with dvi and that doesn't work either. Any help would be greatly appreciated. 


I believe that the monitor has to be certified for Eyefinity for that kind of setup to work. I'm not sure that dell has any Eyefinity certified monitors, also the monitor may be certified for HDMI 1, and older standard that may not work with that card.

What I would recommend is getting a cheap AMD GPU (to avoid driver issues) and adding it to your current system.