Just because a motherboard has graphic outputs does not mean they're active.
1) On current motherboards, the graphics are part of the processor. If the processor does not have integrated graphics, the motherboard outputs will not function. What processor do you have?
2) If your processor does have integrated graphics, then there needs to be a setting in BIOS that allows you to enable the integrated graphics when a discrete graphics card is installed.
Since your motherboard does not have this capability, the on-board graphics will not work, regardless of the processor installed when a discrete graphics card is installed.
-Wolf sends