Normally, the BIOS option about whether the PCIe or onboard video is your default video only matters if there's more than one video card in the system. If you remove the PCIe video card then it should go back to the onboard video automatically. I'd think it's something to do with the monitor. Does your monitor have only a DVI input and no VGA? If you have both then the DVI input is probably digital only and you'd have to use the VGA input on the monitor. If you've got only a DVI input then it better not be digital only. The monitor specifications should tell you which kind you've got. You can also look at
this page and compare the cable to the first set of pictures. Unless they've cabled it in a wierd way then you can tell from the cable whether it's digital only.