Precision 7920 does not POST after Memory Upgrade

Not the most likely solution, but try to blow out the memory slots with an air duster / can of compressed air. Sometimes dust gets in the memory slot and prevents it from communicating correctly.

Check the manual on how your 8x 23GB memory modules should be slotted.

https://www.dell.com/support/manuals/en-nl/oth-xlt7920/precision_7920_om_pub/memory-configuration?guid=guid-ce1561c8-88a9-45e3-bc3b-762cbb37e073&lang=en-us

Remove OEM modules and test with new memory modules only to see if the system will accept them.  Then OEM can be added back.

Memory configuration with DIMM slot locations for Precision 7920 tower.

https://www.dell.com/support/manuals/en-us/oth-xlt7920/precision_7920_om_pub/memory-configuration?guid=guid-ce1561c8-88a9-45e3-bc3b-762cbb37e073&lang=en-us

@TheQuickFox​ Thanks for quick reply. I don't think it is dust. Always blow before install. The "wiggeling technique" doesn't help either. Also, I've put them in exactly like the manual. That is 1, 2, 3 and 4 on each CPU. Double checked and tripple checked.

Tried now booting with five modules, which not particularly surprising doesn't work.

Btw, how long does the first boot with memory check supposed to take after installing 256 GB? After how many minutes can I call it a failiure? It is very stupid design with no feedback.

@Chino de Oro​ I've done that. Tried all the modules pairwise. There is nothing wrong with the new memories and the system accepts them individually. They all have the same part number.

I've now managed to get up to seven modules installed on the mobo and boot into windows (after a lot of trail and fails), but after adding the eight it won't boot. Period. I also tried adding seven, boot, shutdown, replace one module, boot, shutdown and then use the module that the system just booted with in the eight slot, only to fail.

I reckon either the socket or the CPU is deffective!?

Otherwise, this system is superwired. Did a full diagnostics with memory test (6 modules) with a successfull result and no errors. Awesome, except when I close the test, the computer refused to boot up again. Had to cut the power and do a couple of power cycles , before it came back up. It seems to be totally random.

Also in CPU-Z don't report timings table for the modules. Is this normal?

I have the exact same system and a similar problem. I am able to populate 6x16GB in all of the white slots (total 192GB) and the system boots up and works. The minute I start populating the black slots (first to 256GB, then to 384GB), as indicated in the manual. It does not boot past POST. Weird things happen. The power LED was white for a while without POST, and then suddenly all the fans came on like a blower. I let it sit for a bit, but am wondering what the deal is?

Update. Took out all the memory modules and re-seated them one-by-one, carefully. Rebooted. It eventually showed the DELL Logo. I was able to confirm that 24 16GB modules are all working and 12 channels are enabled. Has to be my sloppy hands seating some of the DIMMs incorrectly.