XPS 8940 Blinking Power Light 2 Amber, 1 White & No Video After BIOS Update

Since you had tried everything, maybe time to ship 8940 motherboard plus cpu to Dell repair depot for diagnosis (for a small fee if out of warranty). But I am afraid if bios update had bricked the board, Dell depot would recommend replacement of mobo with a new or refurbished board.  If you have warranty left this would save you trouble. If not, time to think about salvaging cpu, ssd, gpu and move on to non-Dell mobo+case.

Good luck.  I very much doubt the issue is due to a bad intel cpu which almost never dies unless overclocked at dangerously high voltage over long time.  imo proprietary a 8940 mobo is not worth it.  Sell the 8940 psu then get a standard non-dell mobo and case might be a way out of the hole.

The computer is out of warranty.  I found an acceptable price for a new i9 10900K CPU, that is also returnable.  I'll have it in 2 days and if it doesn't fix the problem, I will need to decide if replacing the motherboard and falling further down this rabbit hole is worth it.  I'm almost positive though that the BIOS update finished and the computer restarted normally.  I started building my own computers in the 1990's and when prices of pre-built computers made them more attractive, I decided my time was worth more.  May be time to revisit that philosophy.  Thanks for your help!

Always include version of Windows in your posts...

Can we assume you recovered that screw before next time you powered PC on?

Have you tried running the PSU BIST test? How to run self-test without the button on the PSU

Have you tried booting with monitor connected to one of the onboard Intel Graphics ports with video card completely removed?  Onboard Intel Graphics are usually disabled unless at least one monitor is connected to the add-in GPU and the Multi-Display option is enabled in BIOS.

Did you re-seat RAM modules in their slots?

When you removed the motherboard battery, did you press/hold the power button for ~30 sec before reinstalling the battery to make sure BIOS actually gets cleared?

Try creating a bootable USB using the MS Media Creation Tool for Win 10 or Win 11, whichever you have. You can do this on any PC. With XPS 8940 powered fully off, unplug power cord from rear of PC. Press/hold power button for ~30 sec.  Plug power cord into rear of PC. Plug Windows USB you created into the PC. Power on and immediately start tapping F12.  See if you can get the PC to respond that way...

Do you know if 8940 motherboards still available from Dell?  My computer has the 0KV3RP version, which was apparently the earliest batch, from late 2020.  I can only find a few of those on Ebay and Newegg.  I see more of the 0K3CM7 version which is the newest one.  Are they interchangeable?  I think it will probably cost me more to get a new case, motherboard and everything else than it will to just get a Dell replacement board and I don't really have the time to build a new computer.

You can contact Dell Spare Parts at 1-800-357-3355 (USA).  Have  your Service Tag handy. (Don't post it here.)

Motherboard versions should be interchangeable.  Somewhere there's a thread about the XPS 8940 that lists all the various motherboard versions and their release dates...

The computer is running Windows 10.  Yes, I immediately got the screw and set it aside.  I don't think the PSU is the problem because it will start, the fans will run, the video card lights up and it will continue that way until I turn it off.  I've tried the onboard HDMI and video ports both with and without the video card inserted.  The monitor works as I'm using it right now, with my laptop connected to it.  I reseated the RAM and the CPU several times.  When I removed the motherboard battery, I let the computer sit for 15 minutes before attempting to boot again, and I also tried discharging flea power by holding the power button for 30 seconds (no more than 40 seconds, no less than 26 seconds) multiple times.  I've also tried USB drives using the BIOS recovery file (correctly renamed), Support Assist OS Recovery and Windows 10 Recovery.  Nothing, nada, no video and after a minute or so, blinking amber and white lights.  In the absence of video, I've tried starting the computer and tapping both F2, F12 and holding ctrl-esc with and without a string of expletives at least a dozen times.  I just don't know if any of those options are doing anything because I'm flying blind without video.

I called Dell and they have both of the motherboards mentioned, refurbished for $244.00 including shipping.  The guy said "these motherboards don't go bad very often".  Lol, not according to what I've read.  It would be nice to find out exactly what went wrong, but after shipping and the diagnosis fee for them to say "it needs to be replaced" would probably cost much more than it would for me to just buy one.  I just don't see how a Dell BIOS, downloaded from their site and applied to THEIR product can turn a $2,500.00 computer into a $2,500.00 doorstop.  Uh, unless I accidentally flashed my XPS 8940 with my XPS 17" laptop BIOS....ahem....  At this point, I'm thinking that's what happened.

what if the replacement 8940 mobo gives the same diagnostic light code?  I think shipping the whole unit to Dell repair depot for out of warranty repair is more prudent.  at this point there is not enough evidence supporting that a replacement board is the definite solution. ask Dell whether prepaid shipping is included in such repair.

@kwils1  - I tend to doubt you could have flashed the wrong BIOS. It should have warned you it wasn't compatible and/or just terminated without doing anything.

You should run the BIST test. The PSU might be failing under load even though some components like fan(s) and the GPU lights work.  Wouldn't be first time a PSU (coincidentally) failed during/after a BIOS update...

And re-check all the power connections from PSU to motherboard and connections to/from front panel, etc...

Dell Out of Warranty Repair Service

I checked every connection on the system board and nothing was loose, no broken wires and everything is where it should be.  I removed the front cover and everything there looks ok, including the power switch.

After doing about a hundred attempts at starting / shutting down, discharging flea power and pulling the power cord, removing cards, etc, I started to realize that when I remove the cord and fiddle around inside, the computer starts by itself as soon as I insert the power cord, then progresses to the flashing amber / white sequence.  If I then shut down and push the power button to restart the computer without first removing / reinserting the power cord, the PSU green light comes on, the computer tries to start, then shuts down after a few seconds.  Every single time....

My 8940 doesn't have the BIST button on the PSU, so my only option is to remove and reinsert the power cord which just ends up with the computer starting by itself.  So, I removed all of the PSU power connectors going to the motherboard and the video card, then plugged in the power cord to the PSU.  The green light came on, then turned off after about 3 seconds, which I guess indicates that it is working normally.  So, I guess the PSU is working as it should, but something else is interfering with the POST completing?

@kwils1 - But that result could still mean the PSU is failing under load, the load which you removed by disconnecting all those power connectors.

Not sure you'd get very far with the power connector to the video card unplugged, even if the system was working normally. So I'd remove the video card and only use onboard Intel Graphics for any further testing...

Already tried removing all devices and there is no difference.  No on-board video from either the HDMI or Display Port.  I've read literally every thread about the 8940 and even though PSU's are frequently suggested as a possible cause, it seems that they really are not.  I believe that in my reading and watching videos about the BIST, disconnecting the motherboard from the PSU, inserting the power cord and getting a green light that turns off after 3 seconds indicates that the PSU is functioning normally and is able to supply adequate power to a connected motherboard.  It seems that the motherboard has been the culprit in most of the "dead computer" threads, especially if a BIOS upgrade was involved.  Unbelievably, Dell has a warranty exception that if a BIOS upgrade "broke" your motherboard (yes, the exact word used), unless it was specifically requested by a Dell technician, you could be on the hook for the cost of the repair if your computer is out of warranty...even if their website scanned your computer and recommended the BIOS upgrade.  That to me is a huge red flag waving directly at lousy motherboards.