I have just received my brand new Sapphire Dual X 280X (UEFI) graphic card and installed it. However, my computer won't post at all..

My system is:

Windows 7
Asrock 870 Extreme3
AMD Phenom II X4 955
4GB ram
PSU Fortron Green 600W
old ATI 5830...

The fans are running but the PC doesn't post, the screen is black.
If I unplug one 8 pin GPU power supply socket, the screen is still black but the computer runs fine and Windows start..

After looking on google, I am fearing that my motherboard is not compatible with this card. I think that is is due to the UEFI function..
I have found that the standard 280X Dual X GPU has a button in order to switch from UEFI to standard bios, I don't know is this one has also a dual bios?
However, there is a jumper (1 or 2) next to the CFX port, I don't know what is its purpose. I have tried both position, but no result.

I have updated to the latest version of my motherboard bios, and also a clear CMOS unsuccessfully. (I don't have a motherboard speaker)

I have also found that the 870 Extreme3 v2.0 does have a new beta bios which is apparently solving this issue.. but I haven't found anything for this one..

Could someone please tell me if my motherboard is compatible with this card or if there is any chance of making it work..?

Thank you