Help , cannor display my computer on my LCD

Hi to all

I have a PC connect to a decent GTX 550Ti DVI video card and running at a th very high resolution like 2560 X 1680 on my 27" LCD monitor. I want to do some test, so I enable my motherboard bios to recognize my onboard vga card first, reboot PC, now I connect my monitor with a DVI cable to the onboard DVI slot on my motherboard, I see nothing on my screen now. I even insert my GTX 550 video card and no luck.

I even remove CMOS battery and no luck.

May I know how can I fix this problem ??

Please kindly advise ASAP.