Hi,
What o/s is installed?
Check hidden devices in system manager, view, devices by connection, hidden devices,
Is it shown there, If not,
Check BIOS settings onboard vga is disabled,
Have you got the additional power plug fitted to the graphics card?
A o/s reinstall may be required, as it is the o/s not recognising the graphics card, not the motherboard, as it is shown in POST
Can't think of anything else at the moment!
let us know how you get on?
Regards