Dual screen for Dell T630

[ppthelion]

Hi:
Nowadays, I want to connect two screen of the same type for my computer. The system version is 3.10.0-957.21.3.el7.x86_64. There are two ports available, one is HDMI while another is DVI. It have two graphic cards,
[root@localhost vpn]# lspci | grep -i vga
09:00.0 VGA compatible controller: Matrox Electronics Systems Ltd. G200eR2 (rev 01)
84:00.0 VGA compatible controller: NVIDIA Corporation GT216GL [Quadro 400] (rev a2)
when I start the computer, one connected with the integrated video card works well while the other one connect with the individual video card shows a twinkle circle at first and then turns dark before the login window appears.
In the control panel, under the "display" menu, I can only see one monitor. when I run the xrandr command,also just one monitor comes out:
[root@localhost vpn]# xrandr -q
Screen 0: minimum 320 x 200, current 1600 x 900, maximum 4096 x 4096
VGA-1 connected primary 1600x900+0+0 (normal left inverted right x axis y axis) 531mm x 299mm
I totally have no idea what to do now, any suggestions will be greatly appreciated.

[stevemowbray]

The best idea would be to disable the built-in graphics in the BIOS and connect both monitors to the nVidia.