I, too, have the same issue. And even downgrading the BIOS will not help. I've purchased now 4 sets of memory that is "supposed to" be compatible, but no combination will work without the factory installed RAM in the combination. But once booted into a combination with the factory RAM, no errors were detected in any diagnostic. Contacted Dell Support and they told me would need to have 2666MHz or 2933Mhz... However, all purchased RAM were capable of meeting this specification. In fact, I even mirrored all specs of the factory RAM, but none would boot in standalone or otherwise without the factory RAM.

Dell Inspiron 3891 seems to have a popular Dell ram configuration of 12GB (8+4 dual channel).

Yes, I have matched the above to a tee, minus the size. Every last 16GB or 32GB memory stick does not work. Of the many variants that I have tested, these are amongst the ones that did not work, but should have: Silicon Power SP032GXLZU320BDAJ7, AData AX4U3200716G16A-DBZ, Klevv KD4AGUA8M-32N220A... and now Crucial CT16G4DFRA32A (which was recommended by Crucial System Scan and guaranteed to work). However, it appears that BIOS update 1.3.1 has broken something that prevents me from using any memory not factory installed. I suspect it has broken support for any memory stick greater than 8GB.

is there any way to get back to 64g?

i had the exact same problem

i have 64g kingston fury and when replaced them with factory 8g i was able to boot and had no problem - support was generally useless. any ideas on what memory to purchase (even if from dell) to get back to 64g?

Re: get back to 64G

here are Dell validated OEM 32gb and 16 gb with original manufacturer model numbers.  2x32 gb or 4x16 gb.  Inspiron 3891 has only two DIMM.  So you can only do 2x32 gb.  I do not think you have to buy from Dell ram which is merely validated and quality controlled OEM ram made by various name brands and relabeled by Dell selling at premium price.  As long as you buy your ram with model number matching Dell OEM exactly I think you would be fine.  User benchmark or feedback is helpful too.

732YD 32GB DDR4, 3200MHz, 2Rx8, Unbuffered, 288 pin, Dual Rank, 1.2V, Non-ECC, Non-Encrypted, Hynix HMAA4GU6AJR8N-XN/HMAA4GU6CJR8N-XN, Micron MTA16ATF4G64AZ-3G2B1/MTA16ATF4G64AZ-3G2E1, Samsung M378A4G43AB2-CWE

DK8NX 16GB DDR4, 3200MHz, 2Gx64, Unbuffered, 288 pin, Single Rank, 1.2V, Non-ECC, Non-Encrypted Adata AO2P32NCSV1-BEVS, Hynix HMAA2GU6AJR8N-XN/HMAA2GU6CJR8N-XN, Kingston KDK8NX-MIB/KDK8NX-MIE, Micron MTA8ATF2G64AZ-3G2B1/MTA8ATF2G64AZ-3G2E1, Samsung M378A2G43AB3-CWE/M378A2G43BB3-CWE

re: i have 64g kingston fury and when replaced them with factory 8g i was able to boot and had no problem

if you currently have 72 gb single channel working now, it is pretty good.  64gb double channel is not necessarily better than 72 single.

I stand corrected. The Crucial CT16G4DFRA32A 16GB card worked. Still, though. It'd be nice to have it working with the other RAM I had before again... or for that matter have a better compatibility range... not just a few options here or there.

This happened to me last night.  The most frustrating part is having to have the original 8GB Ram card in order for my machine to boot successfully.  My system was working fine and is less than 3 weeks old.  If I use one of my purchased 16 GB Crucial Ballistix cards with the original * GB Ram card, it works.    I also downgraded the BIOS, which did nothing. Dell customer service was not successful and wanted to set me up with a software call @$99 with no guarantee of a resolution.  Finally was able to get a replacement shipped out to me, which will probably do no good at all.  My guess is that I will have the same issue, but it is worth a try.  Dell support was absolutely worthless.  Spent over 2 1/2 hours on the phone with 6 different people.  I am hoping this gets resolved soon.

Yes exactly the same issue. Had 2 16Gb sticks. Now had to install original memory.

Come on DELL

Ken