Strangest problem ever M4A78 Pro, Sapphire HD4890 and Asus VW220T

Hello, I have got a very weird problem. I work for 10 years in IT now and i've built hundred of systems. So yes, i connected the cables correctly, and no, a reboot doesnt work. It cannot be a driver issue because it happens in POST so before Windows boots....

First i built the system without my ATI videocard. When i connect my screen through DVI i get "No Signal". Then i connected it Through VGA and everything is ok. Then there are three things possible. The dvi cable is defective, the dvi connector on the mainbord is broken or the dvi connector on the screen is broken.

I tried another cable but no effect. So i took the screen to another pc and it worked perfectly. So i thought it's the onboard dvi thats broken.

Then i built in my Sapphire HD4890 and when i connected my screen i got a "No Signal" again. When i put a DVI > VGA converter between it and connect my screen through VGA it works like a charm...

So it isn't the DVI cable, It isn't a driver issue, it isn't my screen, it isn't the ati card and it isn't the onboard DVI. So what the hell is????

A bios update didn't work either....