Right, so here's what happened.

The crucial ram I bought, I bought a little too fast: it was UDIMM, not RDIMM.
So I bought SK Hynix modules with a model number identical to RAM known to be compatible.

And that leads me straight back to square 1:  Power button blinking error code '2,7'.
I don't see anything else than a bad motherboard or bad memory control pin on the cpu.

I guess I'll either sell everything out of spite or gather the strength to walk in a PC shop.

Dell BIOS Updates 

There's a few ways to update BIOS.  One is download it to a flash drive and then boot from it.  See instructions for full details.  I think a PC has to be working to some degree to update BIOS.  Everything has to go perfect as to not brick MB.  You're idea of temporarily going with an older CPU to see if it works, then update BIOS, might not be a bad one.

You could use a working PC to download BIOS, but then I don't know how you would be able to flash BIOS without seeing a screen.

Sure has been a lot of work to get a barebones PC working.  Remember I mentioned possibly replacing the MB?  Might want to compare cost of that to older CPU.  I'm sure the CPU will be cheaper though.

So I get you cannot update the BIOS if you can't get through POST first...

And yeah, a motherboard would be about 150-200€, an old xeon v3 is 50 cents on aliexpress. It will just take a solid month arrive.
The other reason I don't want to change the motherboard is I might change it and end up with the same problem, I can't make sure for certain that the MB is the issue here. Also if it was the issue, I find it weird that 2,7 ram failure would be the first error I get.

Doesn't sound like it's any fun to order anything where you are.

I'm out of ideas for this and 2 other threads with T7910 RAM and other issues that have gone unsolved.  Exception might be if anything changes.  So I escalated this and the 2 other threads.  If they get responded to, it might not be until Mon.

Hi all, just got a 7910 and running into a similar issue. The machine came with 2x E5-2637 V3 CPUs and 32GB ram (8x 4gb Hynix 2133 RDIMM). It booted up fine when I fist got it yesterday, but after updating the bios via Windows, I got a memory power failure and no boot to bios (2, 7 blinking amber lights). After messing around with ram configuration, I was able to boot fine again by removing 1 ram module from CPU 1, DIMM slot 2, and leaving the remaining 7 in the appropriate slots.

What's more bizzare, I tried putting the 8th RAM module in CPU1, DIMM slot 6 (which should be the same channel as CPU 1, DIMM 2), but got the same issue mentioned above: a solid white on/off led but no boot. It tried the module in other slots (CPU 1 DIMM 7) and it worked fine again!

As far as I can tell, it mean the machine has an issue with any ram in that specific slot and channel.

I'm at a loss here. Given that this issue only occurred after updating the bios, I'm inclined to believe it is not a hardware issue. Would love to hear anyone else's experiences.

Note: I have not tried resetting CMOS or replacing the battery yet

Will it let you downgrade BIOS?  Then you might try to update BIOS via flash drive and see how that works, if it makes any difference.  How to flash the BIOS on a Dell Desktop or Notebook with a USB thumb drive .

Hi

I, today, am a bringer of great news!

So I bought an overpriced 2620v3 for 15€ so I could get it locally (France) and faster.
I swapped it in. Instant boot.
Updated the BIOS from good'ol A06, which indeed doesn't support Broadwell v4 cpus, to shiny and latest A34.
Swapped the faster boi back in. Boots no problem.

Huge win.

I've successfully built myself a Bi-xeon, dual Titan, beast of a workstation for 600€.
I've now got it fully working with everything I need, and I'm yet to have any trouble with it

Many thanks for the help !

Glad you got it working!!  Took long enough.  : )>

It's not often the CPU is the problem.  It's more rare compared to other components that can go out.  But when it is the CPU, sure does make things challenging and difficult to diagnose from afar.

So I saw your accepted solution post and thought you said you had it working.

Flashing BIOS won't work without a monitor.  A couple of methods below:

How to flash the BIOS on a Dell Desktop or Notebook with a USB thumb drive 

Flashing the BIOS from the F12 One-Time Boot Menu 

Just to add to this, i've also just bought a T7910 and have the same problem.

Except mine came with an E5-2620v3 already. In my case i've bought 3 x 64GB Hynix LRDIMM's (from 2 different sellers, and i get the same (2,7) flashing amber error when any module is inserted into Slot 1.

I've tried Slot 1 on its own, Slot 1 and Slot 2 and Slot 1 and Slot 5. The only way i can bypass the (2,7) error is by removing the module from Slot 1.  The amber light clears, but unfortunately then i get no video. It was sold as a working machine, but with no RAM supplied. Pretty unlikely all 3  modules I have (from 2 different sellers) are faulty, and given other's issues with Slot 1 i suspect something else is going on. 

Not sure what to try next other than smaller RDIMMs, but i bought this box specifically because it took the larger LRDIMMS. Anyone any suggestions? :-)

Hello,

I would suggest to get 2 x 4gb modules just to have it posting > check the bios version and if needed upgrade it > then check again the 64gb modules