I've done a lot of research on this and seen several posts both on this forum and the amd ones, but nothing seems to be working. 

When I first built this rig on Saturday, I had 128GB Corsair Dominator Platinum but read that that wouldn't work as it wasn't officially supported by either AMD or Asrock, but that the 128GB GSkill Trident Z RGB kit was (https://www.newegg.com/global/uk/Product/Product.aspx?Item=N82E16820232631) so I purchased this as well. (I'll RMA the corsair stuff now)

Alas, I can't get the system to POST with all 8 DIMMs occupied. Slots 1-7 work fine, and I've tried using just 4 DIMMs in quad channel with the 4th DIMM occupying the 8th slot on the mobo so I know the slot is working. With 7 modules installed, windows can see 112GB but only 79.9gb is usable with the rest being hardware limited. I've also tried swapping out the 7th DIMM with the one that would be in the 8th slot, and that works fine, so I know all the modules are functioning.

I've tried unchecking the maximum memory setting in msconfic -> boot -> advanced -> maximum memory. It's what got me to 79.9gb usable actually - up from 62gb. 

Is there some setting in the BIOS that I'm missing? Or some way to make it work from Windows? I know that this kit is supported by the CPU as I saw a Linus video where he used it but on the ASUS Zenith Extreme mobo, so I know its a mobo issue. 

I'm tearing my hair out over this. I've spent so much money on RAM recently it's ridiculous and I can't really afford to buy more if this kit for some reason doesn't work.

the problem always seems to come down to setting up the ram

it may be worthwhile to load 4 sticks set up the timings and then save exit and load the other 4 sticks

lets just say 128gb ram on any threadripper is a challenge to get working

are you south of the river ?

How do I go about setting up the timings in the BIOS? 

I've read so many issues people have been having with 128gb yeah. It's a nightmare. I've spent so much on this RAM though it has to work!

And yup, I am South of the river! Southwark. 

make sure all ram stick are sitting properly (push em hard)

also make sure u dont have any bent pins (cpu)

as above then

if your still not showing 64gb with 64 gb inserted

this sounds more like ram sticks not fitting well (this has been common among all new ryzen based systems) allthough kerberos has a good point about the cpu fitting/pin issue

im over by norbury myself ,it wouldnt be the end of the world to be able to link up if you need my help

setting up ram in bios is a case of running a program called 'ryzen ram calculator' this fine tunes the ram settings to suit am4/tr4 rather than intel,but it sounds like we need to cure the hardware issue first

I actually bot a BSOD last night when i tried setting the max ram in msconfig to 64GB (it defaulted to the maximum after I unchecked the greyed out maximum memory box) I restarted and endless BSOD loop with multiple error codes. I remember one of them being BAD_POOL_CALLER. The only resolution was to reinstall windows. I haven't installed much on this machine yet so no biggie.

I'll check the CPU pins. Gives me the willies pulling the cooler off though. One thing to note: when installing the CPU it did take a lot of pressure on the first screw on the retention plate to get it to bite against the mobo. Apparently this is a common issue as well? I read on here about people having to use undue force to get the screws to bite. Could this have caused it? 

Thanks for the tips so far guys. I'm really grateful.

Thanks for your reply. I have yet to check the pins on the mobo but I will do so. Since they come kinda bent in formation as is, how can you tell if they're bent or not? 

http://forum.asrock.com/forum_posts.asp?TID=2177&title=straightening-cpu-pins-made-easier

sometimes cleaning contacts help. i am using stiff erazor, wipe dirt off and clean with 90 % alkohol, lower  70% will also work but one must wait a bit until water dried.
good to know this problem since i was about to invest in a taichi X99. same problems there?
collegue using a PC with 1200 usd-processor. 64 gb ram is enough then. 3DVR stuff. Ultraquick running PC.

I first tried with 64GB installed in quad channel as per the mobo documentation, checked system information and BOOM all 64GB available, no more hardware reserved bullsh*t. Then I restarted, installed all 8 DIMMs thinking there's no way this is going to even POST, but it did! Booted up all fine and low and behold in system information and task manager, all 128GB available. It WORKS! 

I have to assume that reseating the CPU did the trick, because that seems the most likely solution given the advice, but in reality I rebuilt the system from scratch, so it could have been anything I guess.

This is not to invalidate all your awesome advice at all. I'm pretty sure it was reseating the CPU that was the solution. Thank you all so much for all the help. I am so excited to be able to get down to some proper hardcore particle simulation! (what I built this thing for)

THANKS!

excellent

i would bet it was reseating the cpu as well

and as said already

thank you for updating the thread it does help others in future