You don't get any of those 1 2 3 4 leds?

How far in the boot process do you get basically?

There is some command for trying to get into the NIC "bios" during boot, can't remember it clearly, maybe it was Ctrl-P

Does F12 work? Do you get the boot selection menu? (and the ability to flash the bios by using a USB stick)

Just for reference, my T3610 does this:

Plug into AC:
1   3     (power button is yellow)
     3 4  (power button turns white)
     3

Turn on the computer:
      3 4  = Memory subsystem configuration activity is in progress
      3     = CPU configuration activity is in progress
1 2 3     = Indicates routine system activity subsequent to video initialization
   2 3 4  = USB subsystem configuration activity in progress
   2        = PCI device configuration activity is in progress
1 2        = System resource configuration in progress.
1 2 3     = Indicates routine system activity subsequent to video initialization.

and then those number leds turn off and it boots into windows

Hello, your boot LEDs match mine exactly. After the 1 2, 1 2 3 sequence - yours boots to windows while my system will hang at black screen.

I have tried F2, F8 and F12 to get into BIOS with no avail. I will try Ctrl + P.

The system has been sitting in a corner since starting the thread with the CMOS battery out, hoping the board would clear itself over a couple days off.

Ill attempt accessing the NIC and report back. Thanks

Come to think of it, maybe Ctrl-P is for accessing the Intel Management Engine settings, not the NIC bios.

But yeah, try that and see if it's any use I guess. Not all computers have Intel Management Engine enabled, I think it will have a sticker inside the computer saying "ME DISABLED" if it is not available on your computer.

Is the Windows on the SSD installed in UEFI or Legacy mode?

Also have you tried a different keyboard

I had Win10 installed as UEFI and the PC would boot to Win Boot Manager.

After taking the CMOS battery out for 48 hrs, no progress on clearing the BIOS. I have tried the MB jumpers previously as well. Im stumped as to why none of these could revert it.

I have tried another keyboard with no luck. I have found, if I press nothing during boot, it will go through the sequence of LEDs successfully, the LEDS will go out and I am left with a white solid power LED, as if Win10 was initialized but I am left with a black screen. If I press F8 or F12, the computer will get stuck at the last 1 2, 1 2 3 part of the boot sequence and the 1 2 3 will remain illuminated.

Ill have a PCIE NIC to try on Monday. I think that will be my last hope! Fingers crossed.

One last ditch cheap effort might be a new size 2032 CMOS battery.  They last around 5 yrs. and the T3610 goes back to 2013.  Low battery can cause all sorts of seemingly unrelated problems.

F2 for BIOS if BIOS works again.

I have learned a lot through this experience.. I began removing as many peripherals as possible, optical drive, extra ram, second hard drive. Swapped out graphic card, bingo. Secure boot and Quadro didnt agree for whatever reason, worked fine with an RX480 I had thankfully. I had no idea nvidia could have a secure boot conflict like that.

Sorry if that should have been painfully obvious. Thankfully for people who depend on computer expertise to keep their work going, IT is not my day job! Tinkering with these is just a productive hobby, thanks for all of the input to solve my issue!

I've heard of some GPU's requiring Secure Boot off, but didn't know that they don't even let you into BIOS.

Thankfully on a hunch the RX480 worked, I tried a few other Nvidia cards with secure boot enabled and had no luck with any video output.  I cant say I fully understand it but once I disabled Secure Boot, cards worked with the computer across the board. I thought with Secure Boot, you only needed an official driver release to be installed but I can say with certainty it is much more complex than my imagining of how it operates

What an unexpected solution

I had no idea gpus could do that, my Quadro K2000 plays nicely with Secure Boot.

Glad you got it sorted!