BenQ xl2420t --Seriously need help!--(can't enable 120hz at 1080p)

Yet another thing has gone wrong with my gaming setup   I looked everywhere, and could not find the solution, other people had this problem, but there solution was not mine   should i return the monitor? or is the problem easily fixed? getting the full 120hz is vary important to me, because i play fps competitively.

---~~The actual important stuff~~---

Ok, I have dual msi 7970 lightning graphics cards, the top one is attached to my BenQ xl2420t (1080p 120hz) monitor with dual link dvi (I am using the cable that came with the monitor) I cant get it to run at 120hz

--what I know--

-it is definitely dual link dvi. it says dual link on the actual cable, and it has a full set of pins that plug into the slot labeled dvi-d on the monitor

-I can only enable 120hz at resolutions of 1024x768

-when I arrange the cable different ways sometimes it doesn't even give me the option for 120hz at any resolution ~AND~ I tried plugging it into the bottom card and the monitor didn't recognize it (something to do with the pci slot maybe?)

-I am running windows 7 64-bit

- am using ccc

-I am not sure if i have the benq driver, because it doesn't show up on the start menu, but when i try and update it it says its already up to date???

-everything else about my monitor works fine


I seriously cant figure this out on my own! Thanks in advance!