|"The board model is a GA-M55SLI-S4."|
There are two revision series of the GA-M55SLI-S4 mboards - Rev. 1.x, and Rev 2.x
Mboard manual for Rev 1.x
Starting page 17 of the pdf or the printed manual
You MUST set the SLI jumper on the mboard to SLI mode - otherwise the second PCI-E X16 slot is disabled.
If you don't want to use SLI, don't connect the separate jumper between the cards (that may not work anyway when the video chipsets of the two cards are different).
Bios Setup settings
starting page 38 of the pdf or the printed manual
Make sure Init Display First is NOT set to PCI
[The card(s) will still work in Windows if that is set wrong, but Windows won't be able to use the advanced features of the card(s).]
Mboard manual for Rev 2.x
The same things - starting page 19 and page 40 of the pdf or the printed manual.
"I suspect the drivers have been installed."
OK , I'll assume they have been.
"Under display adapters I have only one entry for the primary PCI-E card."
You should have two entries, or two sub entries, for the primary and secondary graphics controllers on the card because it has two monitor ports.
"I'm not sure on the drivers - the PNY tech had me download and install the drivers for the 9500 and he said those drivers would work for both cards. I don't know if he is accurate."
The same video chipset drivers from the same chipset maker often support many different video chipsets.
You are less likely to have video related problems when that's the case.
Did you un-install previously installed NVidia video drivers and associated programs in Add/Remove Programs BEFORE you installed those drivers?
You MUST do that to get Windows to load basic VGA drivers, and have the card (display adapter) in a basic VGA mode, THEN you install the specific drivers.