I am currently running a custom build with a Sapphire AMD 7790 GPU. The GPU has 4 ports in the back - two DVI, one HDMI, and one DisplayPort. I had my build running fine with three monitors (two DVI and one HDMI), but I recently got a fourth, and it seems like 3 is the limit.
When I connected my 4th monitor, I used a passive DisplayPort to HDMI adapater. I did a little preliminary research, and it seems like AMD cards can only support a select number of "legacy" outputs (HDMI/DVI). So I went out today, and bought a straight DisplayPort to DisplayPort cable since my monitor had the input. However, it's still not working for me.
There isn't a descriptive error - it just says "The display settings could not be saved..." but still recognizes my fourth monitor.
I don't think the problem is with the amount of pixels - I changed all monitors to the lowest output resolution, and I still couldn't extend my desktop to the fourth. How might I go about diagnosing and fixing this issue?