XPS 8940, two ram slots not working

yes if the cpu socket pin is bent it can take out some of the memory slots.

although unlikely in a new pc, that is still one of the common cause of 2/4 slots not working.

Thanks, I will pass this onto Dell support to see if that is the issue

@mrglwatson If you have been using the PC for 6 months without any problems before this and you have not been poking around inside your PC I would say you have a motherboard failure. One more thing you could try is clearing the CMOS with the memory installed in slots 1 & 3.

Are you numbering physical RAM slots from CPU or using their assigned motherboard DIMM # ?

With only one RAM module installed, it should be in 2nd physical slot from CPU (DIMM1). So may not be surprising it won't boot with only a single module in 1st physical slot from CPU (DIMM3). 

When you install a second module that matches the first one in DIMM1, the new matching module should go in 4th slot from CPU (DIMM2). 

The XPS 8940 has some RAM quirks, so it may also not be surprising it won't boot with RAM in physical slots 1 and 2. So try the same pair in physical slots 2 and 4.

Hi Ron,

when I got the PC the single stick ram was located in the second slot away from the CPU, the white latch which I believe is numbered Dimm 1.

This fails with memory error.  With advice from support, I moved the ram into each socket in turn.  The only sockets where the PC would pass POST was when it was in Dimm 4 and Dimm 2.

Support sent me a replacement stick of ram and following support instructions I tried one ram stick in Dimm 1 and one in Dimm 2, this  failed with a memory error.

I did try each stick individually and they both worked when place in Dimm 2 or Dimm 4, so I am confident its not an issue with the ram sticks.

@Vic384​ 

The PC has been sitting in its box unused for 6 months.

the dell 8940 is new (6 months old but unused) 
is it possible that this is a refurbished 8940?

@redxps630​ How would I tell?  It has an I9 cpu (my other 8940 has an I7 and that's about 18 months old).

I also tried swapping the ram on my other 8940 into the newer machine, populating the same slots, but with similar memory fault reported.

@mrglwatson​

Hi Ron,

when I got the PC the single stick ram was located in the second slot away from the CPU, the white latch which I believe is numbered Dimm 1.

This fails with memory error.  With advice from support, I moved the ram into each socket in turn.  The only sockets where the PC would pass POST was when it was in Dimm 4 and Dimm 2.

Support sent me a replacement stick of ram and following support instructions I tried one ram stick in Dimm 1 and one in Dimm 2, this  failed with a memory error.

I did try each stick individually and they both worked when place in Dimm 2 or Dimm 4, so I am confident its not an issue with the ram sticks.

That does sound like a motherboard issue.  You may want to reset BIOS as @Vic384 suggested. With PC unplugged, press/hold power button for ~15 sec. Then remove the motherboard battery and press/hold power button for ~30 sec.

Install the pair of modules in Dimm1 and Dimm2 (slots 2 and 4) and then install a fresh CR2032 battery (~$3).  Close up and see if it boots now.

To be complete, repeat the entire process but this time, move the RAM to DIMM3 and DIMM4 (slots 1 and 3) and reinstall that same new battery.

If it fails to boot either way, contact Support again for assistance...

@RoHe​ thanks for the suggestion.  I only have a single stick of ram now as I had to return the second stick to Dell, and I don’t really like taking my working 8940 apart.

can I do this reset with just one stick of ram

Yes, put the RAM module in 2nd slot from PC and clear BIOS by removing the battery as posted above, and make sure it boots properly after that.

But, that doesn't clarify the issue: Do all RAM slots work when used alone or when more than one module is installed, which might be an indicator of motherboard problems. 

So, at the least, move the single module to each slot, and clear BIOS after each move to see if they all work...

Hi Ron,

many thanks for your help. I tried the single stick of RAM in all 4 slots, clearing the BIOS between each attempt.

The PC boots fine when the ram is in Dimm4 and Dimm2, but gives memory fault when the ram is in Dimm3 and Dimm1.

I've asked Dell support for on-site support as I don't think there is much more I can do myself.

So there's a probably a motherboard fault with that bank of RAM modules (DIMM1 and DIMM3).

Wait, something doesn't make sense. DIMM2 and DIMM4 are in separate memory banks. Did you really mean slots 2 and slot 4, which are both in memory bank 1?  

Regardless, hopefully a new motherboard will solve the problem for you.  Please let us know what happens...

@RoHe​ Yes Ron, the PC is fine with ram in the two furthest slots away from the CPU, which according to the motherboard manual are named Dimm 4 and Dimm 2.

Support had me produce a video showing the ram in each slot and what happens, which I have now done.  So hopefully we can get a resolution.

Thanks again for all your help.

That is really strange, especially since you cleared BIOS in between each move. 

Sure sounds like it's time for a new motherboard, and maybe a new 8 GB RAM module too, to cover all bases at the same time...

Let us know what they say...