HD 7970 sparkling red dots only in 1 DVI port

[Interleukin]

Hi,
I just bought a new monitor + computer and here is the issue

Monitor: Samsung S27A850D (made to use the 2560 x 1440 resolution)
Graphic card: AMD radeon HD 7970 (2 DVI, 1 HDMI, 2 DP ports)
OS: Windows 8 64-bits
I updated the drivers for my graphic card and monitor

When i plug my monitor using a dual-link DVI cable into 1 of the DVI ports on my graphic card, the image is perfect (resolution 1920 x 1080) but i cannot use the 2560 x 1440 resolution.

When i plug it in the other DVI port things go wrong. I get sparkling red dots everywhere on my screen but i have the option to get the 2560 x 1440 resolution. When i do so, not only are there sparkling red dots but the image starts to shake. The image seems to be shaking also at lower resolution. Depending on which DVI port I use on the monitor, I also get an error message on my screen from the monitor saying: "not optimum mode, recommended mode 2560 x 1440" (which is the resolution I switched to when I got the message).

However, when i use the new monitor on my older computer (OS: Windows XP, ATI 1600 series) i can get the 2560 x 1440 resolution (without updating my drivers) and the image is fine. So the problems seems to be my graphic card.

But when i use an older monitor (BENQ FP222W) in the DVI ports which gives me sparkling red dots on my Samsung, the image is perfect on the BENQ (max resolution 1680 x 1050).

So my question is: What is the problem ? My monitor, my graphic card, or drivers and what should I do to fix this problem?
The goal is to be using the Samsung at 2560 x 1440 without sparkling red dots and a shaking image.

 

[Kari]

for starters I believe one of the dvi ports on the card is a single link and the other is dual link dvi. You'd need the dual link to get 2560 resolution, single link doesnt have enough bandwidth, also the 1680 monitor wont use dual link mode either but single link.
So there might be something wrong with the pins in the plug for the 2nd link, either on the card or the on cable itself.