Graphics card problem

Hi all,
I have a graphics card with issues as below:

I have a graphics card that works fine when my monitor is plugged into it (but it blinks at some intervals).

When the graphics card is inserted and my monitor is plugged to the on-board graphics nothing shows on my screen.

when the graphics card is removed and my monitor is plugged to the on-board graphics card everthing things works as normal.

I want to be able to use two monitors togetherat the same time this is not possible with the above problem.

pls can anyone advice. thanks