EPIA M700 with Radeon R9250 PCI no video signal

[Coudy]

I have VIA EPIA M700 board, case Travla C138. I need due to my 24" flat panel resolution 1920 x 1200. With onboard card I can see some artefacts with this resolution. So I bought PCI card Radeon R9250. I connect it using card riser to my M700 in Travla case. But I have no video signal from my Radeon neither DVI nor VGA (before boot and after boot too). Video signal goes still only from on-board video card. I tryed this PCI video card in another computer, the card was working perfectly immediately.
Please could you help me, what should I set on computer setup or jumper onboard to make my PCI Radeon 92050 to work with M700 board? Is ti necessary to switch off on-board video card first and how should I do it? Thank you very much in advance.
I have latest bios revision 1.03.