XPS 8940, limp mode

Re: Power button is solid white in all scenarios

PSU is good.  MB is good.

uninstall all hard drive and ssd, try if you can get Dell logo video or press F2 to enter BIOS video

if all good, do a clean Windows 10 install on a test HDD

Need some more details here.

Today, my PC had a black screen after I tried waking it.  Not the first time, so I powered it off and back on.  But today, I continued to get a black screen.

When powering it back on, what did you actually see? Black screen immediately OR the DELL Logo and then it went black, Windows Welcome screen and the desktop never appeared and the screen went black?

Each of those indicate a different problem.

I figured the GPU was having issues so I swapped to the integrated dp.  No output.  Integrated HDMI, no output.  Opened the case and removed the GPU, still no output.  Unplugged all my extra drives, integrated dp no output... Integrated HDMI has output.

Just moving the HDMI cable might not work. It depends on HOW the BIOS is set. In BIOS there are 2 video settings:

Video
Multi-Display Enable or disable multiple displays.
Primary Display Set or change the primary display.

As I recall, the first one should be set on and both the discrete and Intel HD750 would be active. Primary set to discrete and the HD750 is not active.

Pulling the Nvidia probably allowed the HD750 to work OR there was a short in the Nvidia card causing the problem and blocking the HD750?

I was able to boot into windows.  I've got a backup going now, just to be paranoid, I have backups already.

Gpuz detects the Nvidia GPU, if I plug a monitor into it windows tries to split the screen, but there's no output.  After the backup completes I'll try the SSD/HDD again, but I'm a bit stumped.

What does "split the screen" mean?

In Windows but what H/W is attached? Everything when you had the black screen except the SSD/HDD? Is that a single one? Is it USB attached or internal SATA attached?

Not sure where to go yet, PSU, MB, both?  Why would HDMI work and Display port won't?  Why do I get no output when the SSD is powered?

Power button is solid white in all scenarios.

If removing the SSD.HD allows you to boot, why do you suspect other parts/HW?

Hard to tell on the port, they are shared, that is both the discrete card and the Intel Adapter ports are connected together.

On my 8940 at least I discovered I didn't have to remove the Nvidia card to use the HD750 (only using HDMI cable), All I had to do was in Device Manager DISABLE the Nvidia card. That did the switch over, and I never had to even move the cable.

Possible the Nvidia card is at fault as its DP port failed? No Nvidia Diagnostic tools for consumers though.