I've been on multiple threads trying to figure this out. I have a few different monitors and only one will work at a time on my computer. I am currently only using the VGA to DVI adapters and only the top port is being recognized. I don't understand why I have two DVI ports if only one works and I don't want to go buy a HDMI converter or mini-port. I'd like for both of my DVI ports to work. If anyone else has had this problem and has any advice at all I'd really appreciate it. I've also reinstalled and updated all my drivers as well. I tried to manually detect the screen too.
Same answer as other forums: only some DVI ports provide an analog VGA signal for backwards compatibility with a simple dongle. Your graphics card has only one such DVI port.
From the specifications for what looks like your card, one is DL-DVI-I (dual link DVI with VGA support) and the other is SL-DVI-D which is single link (can't do 2560x1600) digital only.