Asus VG248QE Problem when playing games or full screen video

i brought two Asus VG248QE and everything was going fine then i tried to play a video on a media player that i can't remember the name (as i've uninstalled it now) of and then an error message from the screen popped up saying "Cable incorrect Please use Dual-Link DVI cable" as well as the screen going really pixelated i then yesterday tried to run dayz and i had the same problem i tried changing in game settings but it stayed the same i'm using two amd 7970 graphics cards instead of nvidia so i don't know if this is the problem or if i need a new cable but i'm not to sure what cable to get as i'm not to good with computers and thats why i am here
Thank you for taking the time to read this and i'll look forward to your replies