Hi all, thank you in advance for trying to help!
System specs: 
EVGA Z370 Classified K : 
Corsair Vengeance RBG Pro 32GB (2x16GB) 288-Pin DDR4 :
Intel i7-8700 3.2GHz LGA 1151 :
EVGA Supernova G3 1000w PSU :
Windows 10 64-bit
 
Problem:
Brand new system refuses to POST (with error code C) with both DIMMs installed in any slot configuration. 
 
Info:
Both DIMMs work independently in any slot but not together in any slots. When installed as the sole DIMM, the RGB lights appear as soon as power button is pressed & the codes cycle through POST and I have a working functioning system. However, once I install the 2nd DIMM in any slot it refuses to boot and the mobo produces error code C. No lights appear on the DIMMs obviously. 
 
I've updated the BIOS to v1.12 (it came with v1.07)
I've triple checked the CPU to ensure I seated it correctly without bending any pins. I even loosened the screw a half notch so the cover isn't pressing down so hard on the CPU itself. Temps are steady around 35 degrees celsius. 
Weird thing I noticed was the BIOS has the DIMMS backwards from my vantage point. When I install a DIMM into the slot 2nd from the left the BIOS recognizes it in the 3rd slot from the left. Its like the board is flipped around. My perspective is the same as pictured in the link above but its seems like the BIOS perspective is if the board was rotated and slot 1 starts from the other side. IDK if that has any bearing on this issue but thought I should mention it for thoroughness. I can provide pics to show what I mean if necessary. 
 
This is an issue I've never run into and I'm wondering if I need to RMA the motherboard or the Corsair dimms or if its another issue. 
From my googleFu, I'm leaning more towards RMA'ing the Corsair Kit then if that doesn't fix it, RMA'ing the motherboard. 
 
What do you think? Thanks in advance for the help!

bcavnaugh
Welcome to the Forum
Page #27 Are you using Slots #2 and #4? 
The Intel
® Z370 chipset supports dual-channel DDR4 memory, a maximum of 64GB and up to 4133MHz+ (OC). You must populate even-slots (2, 4) first. The board will not boot if only odd-slots (1, 3) are populated. See chart below:
 
What is the Model/Part Number of your Corsair Vengeance RBG Pro 32GB (2x16GB) 288-Pin DDR4 Memory?
 

Hey sir, 
I apologize. I had links to every part but it looks like they were removed when I posted. 
Corsair Vengeance RBG Pro 32GB (2x16GB) 288-Pin DDR4 : CMW32GX4M2A2666C16W
 
I'm aware of the even slots (2,4) for dual channel to function so that was how I installed them initially. Its strange that the BIOS thinks the slots are opposite but I don't think it matters at this point since I've tried installing them in every possible slot combination and it produces the same resulting error code C.

bcavnaugh
Code C can be caused by the EPS Cable not being Lock-in MB or PSU Side or a Pin Push Out.
Also your Memory is Not Listed here>
Not saying that it will not work only that it is now listed.
You need 11 or more Posts to Post Links.

Yes sir, upon initial troubleshooting we started looking at the PSU first since error code C referenced the power supply & cpu. I have a cable (actually it came with 2 and I've tried both) for this modular PSU labeled "CPU" that's an 8-pin that's locked into the PSU and a 4+4 pin that are locked into the top left of the mobo. It's not possible to switch the 4+4 end into the PSU because they won't latch (as suggested in the manual). 
 
I was not the one who purchased these parts, I'm simply the builder so I shall research the compatibility. If these are not compatible with the mobo I shouldn't be able to use 1 stick successfully should I? 

bcavnaugh

Lieutenant_
If these are not compatible with the mobo I shouldn't be able to use 1 stick successfully should I? 

Single Channel -v- Dual Channel
Maybe you can find more info here

I think my next course of action would be to grab some RAM off of EVGA's support list for this board.
You're 100% correct. I can't find this RAM listed anywhere for compatibility.
They may have purchased it just for the RGB & didn't cross check. I will have to order new sticks & see if they work. 
Will follow up in the next couple of days once I receive them. 
Thanks for your help! 

update time! 
We purchased a set of DIMMs from EVGA's website to make sure they were compatible:
(CMK32GX4M2A2400C14)
 
Same result. Initially installed into slots 2 & 4. LED light above the RAM on the mobo comes on and error code C. 
As before I tried it in every slot combination possible, all producing same error code. 
Pull out 1 DIMM in any slot, system boots up fine. 
 
Unless there's another suggestion, I'm going to start RMA on this motherboard for a replacement. 
Unfortunately since we needed the system functioning, we installed windows 10 (OEM) which means its attached to this motherboard. 
Are we going to be out that money spent as well or does EVGA cover that in any way? 
 
Any other suggestions? I've never had a mobo arrive with dual channel not functioning. First one for me. 

You can deactivate the windows key from the motherboard by doing this.
It does work, I have does it several times, even with the OEM version 
 
Uninstall Windows 10 Product Key
Press Windows key + X then click Command Prompt (Admin).
At the command prompt, enter the following command: slmgr.vbs /upk.
Hit enter.
 
 
 

bill1024
You can deactivate the windows key from the motherboard by doing this.
It does work, I have does it several times, even with the OEM version 
 
Uninstall Windows 10 Product Key
Press Windows key + X then click Command Prompt (Admin).
At the command prompt, enter the following command: slmgr.vbs /upk.
Hit enter.
 

I did not know about this! Thank you so much! Will definitely use it. 
 

bcavnaugh
Any updates?

Indeed. Submitted a ticket via support as required to process an RMA and referenced this thread. Support thinks there might be an issue with the memory controller & recommends an RMA. I'll be submitting the request today. In order to process it I had to create my own account since I purchased it. Lieutenant has been helping me build it and has been posting for me. We will continue to update but it may take a few days to get this board sent off & the new board in. 
 

 

Lieutenant_
update time! 
We purchased a set of DIMMs from EVGA's website to make sure they were compatible:
(CMK32GX4M2A2400C14)
 
Same result. Initially installed into slots 2 & 4. LED light above the RAM on the mobo comes on and error code C. 
As before I tried it in every slot combination possible, all producing same error code. 
Pull out 1 DIMM in any slot, system boots up fine. 
 
Unless there's another suggestion, I'm going to start RMA on this motherboard for a replacement. 
Unfortunately since we needed the system functioning, we installed windows 10 (OEM) which means its attached to this motherboard. 
Are we going to be out that money spent as well or does EVGA cover that in any way? 
 
Any other suggestions? I've never had a mobo arrive with dual channel not functioning. First one for me. 

Hi there!
 
I had the same issue with Z370 FTW. When installing two ram modules in any combination for dual channel mode, computer would not start with error code 4C during POST. One RAM module worked in any slot and computer started normally.
 
I bought motherboard "NEW" from Amazon, but it was open box and MB was used. RMA would cost me even more than I have spent on purchase, so didn't do it.
 
Long story short: motherboard had bent pins in the CPU socket and I assume those ones, that have to do with RAM's dual channel.
 
I’ve managed to fix bent pins with a…  toothpick. LOL. Installed CPU back, turned ON the computer and – it loaded with no errors during POST!
 
Have a look at your socket pins with magnifier (I did it with my phone camera)
 
P.S.
CPU –
I7 8086K
RAM –
DIMM2: Corsair Vengeance LPX CMK16GX4M1B3000C15
DIMM4: Corsair Vengeance LPX CMK16GX4M1B3000C15
 

I'm sorry for my first post οn Evga community..
I have a question .. the people of technical support read these postings;
 
In our issue now.
I have exactly the same problem with the Z370 FTW motherboard.
I spoke with technical support as usual. 8/4/2019
The first answer:
"Hello,
I apologize for the trouble with your motherboard, this error indicates an issue with the CPU that is installed on the board. Please inspect the CPU and the socket for any damage or bent pins. If possible test the CPU on a different motherboard. Please let us know if we can address future questions."
 
I spoke with technical support again on 10/4/2019
The second answer:
Thank you for contacting EVGA Support.
Please find the following CPU and Memory compatibility list from following link.

These Two models (CMW32GX4M2A2666C16 & Corsair CMK32GX4M2A2666C16) are not listed under compatibility list for this Maim board.
 
I spoke with technical support again on 11/4/2019
The answer:
Thank you for coming back, the Main board is tested with only available list of memory module from the following link.

Sorry to say, we do not have data of test results from other memory modules, unfortunately.
Please feel free to contact if you have any further question.
 
Then I searched I searched and I bought other most compatible Dimm's
I had been waiting for several days because it was relatively rare and expensive to receive.
Yesterday, 16/4/2019 the new dimm's came  but the result was again the same and worse.
Ι send again email on EVGA technical support and I hope soon to be able to replace the motherboard.
 
After all this history i found this post.
and the Question is.. the people of technical support read these postings;
What technical support is this when the buyer finds the solution alone ?
Why did I waste so much time (days) and money ?
 
Sorry for my bad English i use translator.
I hope this time I will have soon a Support Ticket Number to be able to replace the damaged motherboard.
 
Thank you.