I am getting a warning and then an error that I can not understand.
upon starting the cursor looks like an X then goes to a regular arrow. Assuming when the cursor changes is when the Screen 1 is deleted.

After grepping the /var/log/Xorg.0.log file I find
(WW) MGA: No matching Device section for instance (BusID PCI:3:0:0) found
and then the associated error;
(EE) Screen 1 deleted because of no matching config section.

I have a
Section "Device"
Identifier "NVIDIA Corporation NV17 [GeForce4 MX 420]"
Driver "nv"
BusID "PCI:1:0:0"
That is working just fine, it came with the Dell computer

I added the matrox card manually after running lspci(0000:03:00.0 VGA compatible controller: Matrox Graphics, Inc. MGA G400 AGP (rev 85))
Section "Device"
Identifier "Matrox Graphics, Inc. MGA G400 AGP (rev 85)"
Driver "mga"
BusID "PCI:03:0:0"

I have two monitors that are the same so only described them once.
Section "Monitor"
Identifier "Q71-6"
Option "DPMS"

Defined 2 screens;
Section "Screen"
Identifier "Screen 0"
Device "NVIDIA Corporation NV17 [GeForce4 MX 420]"
Monitor "Q71-6"
...

Section "Screen"
Identifier "Screen 1"
Device "Matrox Graphics, Inc. MGA G400 AGP (rev 85)"
Monitor "Q71-6"

but the warning says a screen has not been defined.
I left out what I thought was extraneous lines in the above descriptions.

I am at a loss to understand what to try next.
Trying to use only one port of the dual port card at this time. If I can get over this hurdle will try to hook up the third.