Hi Digitalmedia34, did you solve this? Facing the same problem...  Trying to install an Asus GT730-2GD3...  

Digitalmedia34 Did you manage to solve this? Any help appreciated. Regards.

Did you manage to solve this?  Facing the same isssue...  Any help appreciated.. Regards.

Ok, in case is of use for someone. I managed to get it working with: Bios 2.4.2 . Just plugged in an Asus Nvidia GeForce GT610 in Slot 3. Didn't disable onboard video(as all suggested). Booted into Windows 10 where the card was recognized. Downloaded all the appropiated drivers from Nvidia website, all perfect, video showing great. It even managed the other monitor plugged into the onboard card(dont know why).  When booting I see video on a monitor still plugged into onboard card, when in windows I can choose where and how to see video in both monitors.  Just be cautios in properly seating and securing the card, if it unseats even a little, for instance, when you are pluggin your hdmi cable, it will bring trouble.  Good luck.

I tried Torrenegra solution and it works just fine. I bought Radeon HD6450 because it has support for windows server 2012 which is what I am running.

The 12th generation servers T320/T420/etc.. have UEFI bios (GUI bios with links and mouse support).

Most modern monitors provide at least 2 input - 15pin VGA DSUB and DVI-D or HDMI or DisplayPort.

Method A:
Leaving the onboard Matrox VGA enabled and connect a VGA cable to
a) F2 - enter the Bios,
b) F11 - BIOS/UEFI boot,
c) access Windows Boot manager (not an issue if only only OS installed)
while Windows GUI is displayed via Nvidia/AMD-ATI using DVI-D/HDMI/DisplayPort cable

After installing Nvidia or AMD video cards at the PCIe x16 slot, proceed to boot Windows where it shows up on the VGA screen (using the onboard Matrox). Windows Device Manager will show 2 items under "Display adapters". Both maybe "Microsoft Basic Display Adapter". Connect the Digital Output (DVI-D/HDMI/DisplayPort) cable to Nvidia/AMD-ATI adapter. Install the appropriate Nvidia or AMD-ATI display driver for the OS. Reboot.

The VGA screen would show the Bios splash screen then goes blank. Switch the monitor to the Digital/DVI-D/HDMI to see Nvidia/AMD-ATI output. You can disable "Microsoft Basic Display" and leave Nvidia/AMD-ATI adapter as the main adapter.

Method B:
Disabling the onboard Matrox VGA in the Bios menu would give you a blank screen if you try to
a) F2 - enter the Bios,
b) F11 - BIOS/UEFI boot manager,
c) access Windows Boot manager (not an issue if only only OS installed).
You still can see the Bios boot process such as AHCI, Perc H710 or you can access H710 Bios .

It seems that there is a compatibility issue between Dell server UEFI Bios and 3rd party video cards regarding displaying the UEFI Bios options and configurations. I doubt that the Legacy Video Option ROM or UEFI Video Option ROM of Nvidia/AMD-ATI adapters are compatible with Dell UEFI bios. There is UEFI GOP - Graphic Output Protocol but little info are provided by Dell and Nvidia/AMD.

My system:
Dell T320, bios 2.6.0, UEFI boot -> internal 512MB USB stick with REFINd -> PCIe x4 NVMe adapter with Windows 10 and Windows Server 2012 R2 (dual boot) on Samsung 960 NVMe / M.2

The 3rd party video adapters that I tested with Method_A:
Dell / Nvidia Quadro 600 / 2000 / NVS 310,
MSI Nvidia Geforce GT 710,
EVGA Nvidia Geforce GT 630.

The older PNY / Nvidia Geforce 9400 GT somehow can display the Bios content when using Method_B (disabling the onboard Matrox). In other word it has all the functionality of the onboard Matrox along with nice graphic and DVI-D output. I don't know why the newer Geforce GT 630 / 710 / Quadro 600 / 2000 do not have this capability.

I did two things: first I took the pins out from the 12-pin SCSI tray connector P3 by pushing staples into the connecting side onto the sides of each pin to pull them out. The official Molex Mini-Fit extraction tools looks like tweezers with narrow and long tips. (You need to use wider staples or two together.) I did the same with two 6-pin PCIE connectors, then inserted the pins from the 12-pin into the two 6-pin. There are 6 black GND pins which go onto the side with the clip, opposite from the 12-pin connector. But there are only 5 red ones, they all carry 12V - measured that. I inserted 3 pins into one connector and the remaining two pins into the other connector by leaving the middle connector empty, as this is used for the sense wire on some pinouts. I updated the BIOS to 2.7. I tried with a GTX 760 that came up but reported that not all connectors are connected - this one has an 8-port and 6-port PCIE. I tried an old GTX 275 with two 6-port PCIE which came up just fine. One thing to consider is that the power supply delivers only 550W. With four drives, memory and two processors, there is probably not that much left. I would not go over 150W power consumption. Will test with a few more cards, the GTX 275 was just something that I had. 

Forgot to mention: just fine means, on-board graphic disabled in BIOS, and GPU showed BIOS and boot screens, as well as ESXi shell.

Dell T420, 750W Redundant PSU, Dual Xeon 2420's.

Had same problem. Tried latest bios (firmware) to no avail. UEFI Nvidia cards would display POST but would go black during firmware inits, and after a minute or 2 the server would reboot. AMD cards displayed nothing, though turned on monitor.

As suggested earlier in this post, disabling MMIO ( Memory Mapped I/O for PCI-E ) fixed the problem for me.

My PSU has 2 8 pin PCI-E GPU plugs. I used a pair of spare PCI-E cables from my EVGA modular PSU, and these cables fit and work perfectly fine, no need to mod, screw with pins etc.

I have not tried the AMD cards however, as I am not going to run one anyway in my now video editing machine.

UEFI cards tested - GTX470, GT730, GTX980

Best Nvidia card I have which would run with MMIO enabled was the NON UEFI GTX295 Dual GPU card.

@Digitalmedia34​ Hello, I realize this is an old thread but when I go to disable onboard video this option is greyed out. I am going to clear CMOS with the jumpers and also just in case clear password, I going to report here if I can hopefully sort out this problem

@tonschk​ Yes sort out already, I just reset BIOS with the jumpers easy peasy and I can again as before disable the integrated video and use discrete  AMD Radeon Pro  W5500 graphics