Hello Lewis_H, thanks for joining the Intel Community.
It is important to tell you that some systems do not allow using the onboard video and a video card at the same time. Most of the time, once you installed a Video card on the motherboard; the onboard video gets disabled automatically.
You can try connecting the two monitors to the video card using the ports it has available.
More information at the following link Graphics Drivers — Multiple Displays Frequently Asked Questions (FAQ)