XPS 8940, will not boot with DELL purchased RAM

Thank you! We have received the required details. We will work towards a resolution. In the meantime, you may also receive assistance or suggestions from the community members.

Will share some experience (have i7-11700) ...
My PC came with two of 8GB 3200 1Rx8 (single rank) total 16GB in while clip slots.
I've added two of 16GB 3200 1Rx8 and PC has booted showing 48GB with one exception - frequency has triggered into 2933 mode instead of 3200.
I have tried different configurations swapping black and white slots with new/old sticks or leaving just one new module in - RAM was still operating at 2933 frequency.
In a result just got another pair of the same new modules (this one worked for me: cheap Transcend JM3200HLE-16G from MemoryC, it has SpecTek chips on sticks) and it synced all four (new) modules without a problem at 3200 Mhz (Command rate: CR=1T, Gear2 mode - the only a bit slower part unfortunately, but that's by Intel specification for i7, should have gone for i9 instead for better RAM config), Therefore I assume it was just some incompatibility between two batches from different manufacturers.

There's one note - first boot after changing memory was taking around 2 minutes, not instant as it was before, but after all automatic internal checks BIOS part of boot time (Dell Logo) returned to instant (3-5 seconds?).
Since you're not saying what RAM model you have put in - it's better to be careful and not buy by accident ECC / buffered memory or the one having XMP profile (also brand new from reputable seller works much better / has lower risk, not used one).


P.S.
1) Those configurations you see on specification means what Dell has tested and can assure those work, it doesn't necessarily means other configs won't work, they just can't warranty it will work.
2) Memory controller is located on CPU, although there's some logic on MB (partially BIOS controlled) for powering RAM (voltage regulator for memory, different for CPU).
3) Memory error code normally has distinct Morse sound beeps, therefore not just silent fail (although I think this is probably possible too)

@Bob F. It is possible that one or both of the new RAM modules are bad, although not likely. You should try to install the new modules, one at a time, in DIMM1 slot, the white slot closest to the CPU.

So...after a lot of great communications with DellCares (thank you), and a lot of swapping modules into various slots, it appears that the problem is that the system simply doesn't like a 48gb configuration.

8, 16, 24, 32 and 40gb works (in a variety of configurations), but 48 does not. If I add all 4 modules (48gb), it won't boot, and there are no error beeps or lights, it just doesn't boot.  If I remove any one module from any slot, it will boot.

I will probably buy 2 more 16gb modules, which will fill all 4 slots and get me to 64gb, which is an acceptable configuration, and that will likely be the proof of my conclusion that simply is that 48gb doesn't work.

Have you tried mixing the pairs? Put two matched modules (eg, 2x 8 GB) in 1st and 2nd slots from CPU (mismatched retention clip colors). Then put the other matched pair in 3rd and 4th slots from CPU (again, mismatched) clip colors).

Now remove motherboard battery and press/hold power button on PC for ~30 sec. Reinstall the battery and see if PC boots properly now.

I did mix and match the pairs. Didn't work. I did not pull the CMOS battery, since DellCares did not suggest it.

At this point, I am waiting for a couple more 16gb modules to arrive (tomorrow), and will see if 16gb X 4 remedies the issue.

Since 48gb is not a recommended configuration, it's probably best that I go with something that is recommended.

@Bob F. I must be missing something because I thought you wrote more than once that 2 x 16 GB (32 GB) did not boot. In fact, didn't you write that you can't understand why 32 GB, an acceptable configuration, did not work? Is 2 x 16 GB working now?

Sorry for the confusion. Yes, when I first tried to get this all to work, the 2 X 16gb configuration did not work. Or at least I thought it didn't it seems that after you change something (add memory...) the computer makes noises and lights up as if it is booting up and then shuts down. Apparently you have to hit the power button again, the first time after changing the configuration. I've never seen a PC do that before. 2 X 16gb may have worked from the beginning after all. (note to Dell...your documentation could use some improvement).

All that aside, I do know that 48gb absolutely does not work.

Sorry for the confusion, and thanks for your suggestions.

It's always a good idea to clear BIOS by removing the motherboard battery and pressing/holding the power button for ~30 sec after making a major hardware change, eg, installing additional RAM or moving the modules into different slots. That forces BIOS to see the changes...

No guarantee clearing BIOS will allow 48 GB to work because the two pairs may just not be compatible with each other, regardless of slots.

I just upgraded my 8940 to 48GB total RAM from16GB (2x8GB) with one Crucial 32Gb RAM to the 3rd available slot. It is now occupying on 1,2,3 slots, leaving one empty for future upgrade, if ever.

I have absolutely NO ISSUES whatsoever with adding just the one extra 32GB RAM stick and it boots up fine, of course initially the splash screen notifying me of 'RAM has changed' whether I should proceed or go to BIOS. I proceeded and boot straight into Windows. I then checked system info and it recognizes total RAM (see screenshots).

The Dell spec sheet also stated that it can be installed in this configuration, so I purchased the RAM accordingly (see description below with bold/underlined).

Table 5. Memory specifications (continued)
Description Values
Minimum memory configuration 8 GB
Memory size per slot 4 GB, 8 GB, 16 GB, 32 GB (according to this)
Memory configurations supported

● 8 GB, 2 x 4 GB, DDR4, 2666 MHz/2933 MHz, UDIMM, dual-channel
● 8 GB, 1 x 8 GB, DDR4, 2666 MHz/2933 MHz, UDIMM
● 16 GB, 2 x 8 GB, DDR4, 2666 MHz/2933 MHz, UDIMM, dual-channel
● 16 GB, 1 x 16 GB, DDR4, 2666 MHz/2933 MHz, UDIMM
● 32 GB, 1 x 32 GB, DDR4, 2666 MHz/2933 MHz, UDIMM (according to this)
● 32 GB, 2 x 16 GB, DDR4, 2666 MHz/2933 MHz, UDIMM, dual-channel
● 64 GB, 2 x 32 GB, DDR4, 2666 MHz/2933 MHz, UDIMM, dual-channel
● 64 GB, 4 x 16 GB, DDR4, 2666 MHz/2933 MHz, UDIMM, dual-channel
● 128 GB, 4 x 32 GB, DDR4, 2666 MHz/2933 MHz, UDIMM, dual-channel

NOTE: The computer is shipped with 3200 MHz memory.
However, with Intel Core i3/i5 processors, it is limited to
2666 MHz. With Intel Core i7/i9 processors, it is limited to
2933 MHz.

This is the part purchased: Crucial RAM 32GB DDR4 3200MHz CL22 (or 2933MHz or 2666MHz) 

Original System built:

Dell XPS 8940 (Special Edition)
11th Gen Intel(R) Core(TM) i7-11700K processor (8-Core, 16M Cache, 3.6GHz to 5.0GHz)
16GB, 8Gx2, DDR4, 2933MHz
512GB PCIe M.2 SSD +1TB SATA 7200 RPM HDD
NVIDIA(R) GeForce(R) GTX 1660 Ti 6GB GDDR6
Killer(TM) Wi-Fi 6 AX1650i (2x2) 802.11ax Wireless and Bluetooth 5.1
BDRE Drive (Reads and Writes to Blu-Ray disks)