I have a new build with a SR-3 and Xeon W-3175X CPU and EVGA 3090 FTW Hydro Copper.  4 sticks of Corsair Vengeance PC3000 memory in the documented supported slots.  In a brand new Windows Enterprise 2019 LTSC install on a Corsair MP600 M.2 disk the system hangs randomly while idle.  after looking at event logs I cannot find anything that points to a particular problem.  I have installed 3DMark and run tests... most the time they complete.  every once in a while the system will power off.  I suspected a heat issue and installed Aida64 and logged sensor data to disk.  After running a couple stress tests in 3DMark the logs do not show any temperatures that would be in the danger areas, in fact nothing exceeded 80 degrees centigrade after 20 minutes of stress tests.  I have tested the RAM in the windows memory test without any errors.  I have run y-cruncher and calculated pi to 5,000,000,000 all in memory in a couple minutes, so thinking that memory is not the issue.  At this point I am a little stumped.  I let the system alone for 30+ minutes and it hangs.  I have power management in the OS set to performance and set sleep to never along with the screens and anything else that the power saving mode will effect.
 
Oddly enough, when it hangs,  the mouse and keyboard still work but I cannot perform any tasks like shutting down the PC or opening the task manager.  Control-Alt-Delete will bring up the menu but none of the selections work.  
Anyone have some suggestions?  perhaps a good debugging tool that runs and logs potential events that cause the hang?  I know it is not the video card, but perhaps a driver... 
 
sorry have been up all night beating my head on the desk... let me know if this post does not make sense.
 
-J
 

Thanks Kougar, I have replaced the RAM with faster Corsair Dominator memory and the Video Card is fully inserted and supported by an undermount brace attached to the case.  All software / Firmware / BIOS are confirmed latest.  All Patches have been applied and all unnecessary software has been removed.  I have been running Y-Cruncher which beats up CPU with written results to all available memory.  The Windows Memtest shows no errors and using 3DMark to stress the 3090 has not caused a fault.  
 
It just seems odd that all benchmark and stress tests complete without fail and the system hangs randomly when I am AFK.  Sometimes within a few minutes and others within a few hours.  Last night it did not hang... Thinking software at this point.  Anyone have a recommendation for a debugging tool for windows 10?  The only thing I changed yesterday was to disable the Intel Speed Step... maybe that was it??? one can hope.
 
I am not an expert on all the nerd knobs inside the BIOS.  Seems there are quite a few options that I am not sure I should have enabled... things like NUMA, BAR support etc... I have some research on some of these settings it seems... just started spring classes so my mind is under assault.  
 

Turns out this was a USB peripheral issue.  The Corsair Nexus USB display that is an addon to their keyboard is not ready for primetime.  It is either defective or has bad software.  In any case when it is plugged in and running an event appears to cause the scheduler in Windows to hang.  Mouse works but nothing is selectable and only thing you can do is hard reboot.  Opened a ticket with Corsair.  Seems that this is a known issue.  I unplugged it from my keyboard and it has been stable since.  However the Re addressable BAR update on the 3090 FTW3 introduced this week created a new problem and if enabled in the SR-3 BIOS the system fails to post.  Had to clear CMOS data to correct.  Not sure if this is affecting anyone else though.

hittman
Turns out this was a USB peripheral issue.  The Corsair Nexus USB display that is an addon to their keyboard is not ready for primetime.  It is either defective or has bad software.  In any case when it is plugged in and running an event appears to cause the scheduler in Windows to hang.  Mouse works but nothing is selectable and only thing you can do is hard reboot.  Opened a ticket with Corsair.  Seems that this is a known issue.  I unplugged it from my keyboard and it has been stable since.  However the Re addressable BAR update on the 3090 FTW3 introduced this week created a new problem and if enabled in the SR-3 BIOS the system fails to post.  Had to clear CMOS data to correct.  Not sure if this is affecting anyone else though.

Very glad to hear you got it figured out! Also I apologize, I had missed your reply somehow.  Regarding the BAR issue, did your motherboard include a BIOS update with BAR support? Both the GPU and the BIOS both must support it is my understanding.

I've heard so many horror/nightmare stories about various Corsair software that anything that requires it to run is prohibited from entering my system.