XPS 8940, doesn't boot with extra RAM

Windows update may have involved a bios update without your consent and now the new bios is blocking non-Dell ram.  It is a bug of new bios, not intentional but happens, that is my guess.  Happens w Dell Inspiron latest model.  If you know your previous bios version then check current version and see if indeed a bios update had occurred.  

What Slots are the sticks in?

What size sticks are you replacing them with and in the same slots?

What does this mean, "If I quit them, it boots."? This was before you replaced them, so what did you actually mean?

The 8940 has 2 sets of channels for the sticks:

Which did you have them in, and did the replacements ones go in the same slots?

What I'd try is one stick at a time, see if it boots (BIOS should report a memory difference, ignore it), use the slot closest to the CPU (#5). If they both boot than the DIMM's are good, could be a problem with one of the slots, especially if the replaced RAM used different slots.

Wondering is the Coin Battery was having a problem?

It does sound like a DIMM problem, but taking it to another PC and they work does sort of rule that out? If you were using the same slots, that too might rule out the slot going bad?

@redxps630 

Don't think this is a BIOS update situation? I've used every Dell BIOS on my 8940, and I have the SAME Crucial series, but instead of 2x32GB, I've got 2x16GB.

Wouldn't think the 32GB DIMM's be treated any differently?

That particular series of RAM is what Crucial's website states is for the 8940 when you use the search for compatible RAM on its website..

Hi @ispalten , let me try to explain better, sorry for my poor English, it isn't my native language.

I have not replaced the sticks, I have added new ones. The 2x8GB original RAM sticks are in the 5th and the 7th slots of your picture. And the 2x32Gb ones I bought are (or were) in 6th and 8th. And configured like this, it has been working for a year recognizing 80GB@2933MHz as I show in the following picture.

But now, I can't say if a BIOS update can be involved (Thanks @redxps630 too), but this doesn't work, the computer doesn't boot with the 4 sticks plugged in. I have to remove the 2x32GB to boot. If I remove the 2x8GB sticks it doesn't boot with 32GB sticks in the 5th and 7th or in the 6th and 8th, no way. I thought they may have broken, but they work on another computer. And I have been able to do another test with another 2x8GB, and this way, with 4x8Gb it boots, so I think every slot is OK.

@akedna 

Thanks for the additional info (you English is fine!).

Well, first I think you need to do one additional test. Using ONLY Slot 5, the closest to the CPU, put in one 32GB DIMM and see if you can boot. Then try the other 32GB there... It is possible one would not boot and it has failed (Crucial will replace it).

Now, that said, @redxps630 might have a point about a BIOS change? Why? Well, from the 8940 Setup Manual there is this chart:

Note that 80GB's of memory is not a supported configuration. The keyword is SUPPORTED, that usually only means if you have a different one, Dell will not assist. I would NOT think they'd put a test into BIOS to stop booting though?

No I have 2 16GB sticks from Crucial that I bought on the SAME page at Amazon, so I'd not think there would be a difference between the 16GB and 32GB DIMM's in specifications other than size of the DIMM?

By doing the single 32GB DIMM test it should rule out if there was a failure on one of them? Possible, say, the speed of one on the BIOS check wasn't fast enough, and on the other computer it isn't checked? Who knows?

In any event, you might want to try Crucial's website if none will boot. You can call Customer Support or email them.

However, I just searched HERE and found this Subject, https://www.dell.com/community/XPS-Desktops/XPS-8940-four-8GB-Crucial-ram-no-boot/td-p/8093141/page/2 and it is a VERY SIMILAR problem, and it was SOLVED... the ORDER and placement of the DIMM's fixed it. MAY NOT work for you as you have 2 different sizes of Memory though.

Anyway, do the SINGLE DIMM test and it both boot individually, check the link above and populate like the link had the DIMMs populated.

Still, does NOT explain how it worked before?

Hi!

Thanks, @RoHe, it worked! I had done a RTC reset and I am not sure why, but I thought it was the same thing or that at least, for these types of issues, it should have worked. I have only installed 2x32GB sticks, I can live without those extra 16GB considering the lack of official support.

@ispalten thanks also for your help, I was going to try your advice but I tried @RoHe's first and since it worked, I didn't need yours.

@akedna  - Glad that worked.

You might still try installing that other RAM when you get to step 5, above.  Just because a RAM config isn't "official" doesn't mean it won't work. Dell just didn't validate that config.

If that doesn't work, there's also another possibility:
Put each matched pair of RAM modules in slots with different color retention clips at step 5, rather than in slots with the same color clips. 

Hello, So, I have (2) 8 GB sticks in my 8940, and I am wanting to double it. By this chart, I cannot just add 2 more 8 GB sticks in the other 2 slots? I have upgraded my Bios to 2.12 also.

@Knash63 

Well, that chart IS only what Dell HAS tested and Supports. Doesn't mean it will not work.

I'd bet it will give you 32GB's of RAM even.

One reason I assume is you only have 4 slots. Most people would use large RAM sticks and go higher. Another reason to do that, actually one 32GB stick would draw less power and create less of a thermal load that 4 8GB sticks.

I've got 3 16GB RAM sticks... Original single 16GB (single rank performance) that came with the XPS. I needed 32GB's and wanted Dual rank RAM. So I went to Crucial and purchased 2x16GB and installed them in the White slots. 32GB's worked fine, but I decided to add in the other 16GB... system worked fine, does not list 48GB's either. Still it worked, but I did have a slight performance degradation due to the Single Rank RAM, so I took it out.

If you are sure 32GB's will be all you need, do it. If however you might need in the future 64GB's, I'd buy 2x16GB RAM sticks (Dual Rank) now instead.

@Knash63  - That chart only shows what Dell tested/validated in XPS 8940, and they don't test every possible combination.

IIRC, there are threads saying 4x8 GB will work in XPS 8940, so search for them. Just make sure the added RAM is fully compatible with this PC model and with the existing RAM.

Many users around here buy RAM for Dell PCs from crucial.com because they guarantee it works when they recommend it for a specific PC model, or they'll take it back...

The reason for 4 ram slots has more to do with the price of commercial motherboards than anything else, also non Server boards or HT motherboards only support up to dual channel and not quad channel memory configs.   If you wanted to populate all 4 channels you would use 4 DIMMs of DDR 4 in single-ranked config vs using dual-ranked DIMMs in all 4 slots.  This allows interleaving between all the dims and still is a dual channel. If you are going for dual-ranked DIMMs just use 2 dims of whatever capacity you desire, using 4 dual-ranked DIMMs has 0 benefits. 

Do note that 4 DIMMs Single ranked while still operating in dual channel mode, puts a higher load on the memory controller Hence why most just stick with 2 sticks and higher capacity since ram will just interleave banks on the onboard ram controller. 

Once again this has nothing to do with any thermal load.