Aurora R7, 4x32GB 2666MHz, 64GB reserved

If you really have an Aurora R7 I am not sure how you are getting 32GB RAM modules to work at all.

These days memory controller is indeed embedded directly into CPU for most Intel desktop products and as per Intel' specification for i7-8700 CPU maximum supported RAM is 128GB
BUT
There are so many possible hardware or software related issues causing this problem.
Motherboard manufacturers can impose limitations via hardwired electrical design (e.g. by physical limiting number of slots) or as part of soft configuration (mostly via BIOS).
Since DELL (check specification as previously was pointed out by @ProfessorW00d) hasn't designed your motherboard to support 128GB (despite having x4 RAM slots) - there's a possibility of control being imposed (or not implemented for wider support) on BIOS level (I've read some users sharing experience of unlocking significant chunk of HW-reserved RAM to be available for a system by changing some settings on other motherboards, even resetting BIOS).
Some older CPUs are having troubles with correct memory detection on RAM sticks having newer higher density chips.
Try to run memory diagnostics on each individual module (by having just single one at a time). It might also be a good idea to test a single module in different slots - just to make sure all slots are fine.
This issue might be specific to Windows configuration - to double-check this it might be worth to install different operating system and run checks for available physical memory from there.
There's also manual settings for Windows to limit maximum memory via msconfig.exe
etc... so many options and possibilities.
p.s. my computer says 311MB is hardware reserved out of 64GB (x4 DIMM modules).

 i have put 4 X 32  and the sytem as reserved 64  after i have shutdown and put 2 x 16 come with the aurora and system says reserved 32

Clear CMOS by disconnecting power to the PSU, remove the CR2032 coin cell battery, hold in the power button for 30 seconds, put the CR2032 battery back in place, plug in and power up . . . see what readings you get with the 2x16GB RAM modules.

i have try to clear cmos and 64 of 128 are reserved by hardware

are you telling me that if I do cella The aurora r7 will support all 128 g and apply them even under windows?

Ok and if buy a z390 for same processor i can use totaly or no ?

ITs bios alienware firmware dont allow to use all ?? on the boot the bios detect all the ram when im on windows thats say Detect 128g the ram and   64 g are reserved by hardware when im put all 128 g 

It's not a validated configuration as 128 GB was never validated. so it's behaving erratic because of that. If you put in the original memory modules and do what the professor said, it should come up properly.

Also this is a Z370 chipset and they are limited to 64 GB maximum.

You might want to check out this posting for additional information: R7 

Z370 only supports 64GB (absent a BIOs update which is not available).  Even for third party boards I believe updates for 128GB were only offered starting with z390. You will see 128, but only be able to use 64. The remainder will be hardware reserved.

Also, some others have unsuccessfully tried on the R7. 

no, I am saying it does not support 128 GB memory capacity and is limited to a maximum of 64 GB only.

Most don't support more than 64 GB either.

For example this board, limited to 64 GB also: Asus Prime Z390 

Always look at the technical specifications before purchasing items. A retail board will likely not fit/work in the R7 case due to the OEM design of that case.

Not the board above:

the z390 its say support 128 max