Just in case this is a memory instability problem, set the following in UEFI:
1) Set DRAM Read to Read to 7
2) Set Command Rate to 2T (AKA Command Mode)
3) Set CPU/NB voltage to around 1.30V
4) Set DRAM Voltage (VDIMM) to the specified voltage of the memory used.
After setting those timings, ensure you are running the latest BIOS. Use one memory module to update if the system is very unstable.
I assume the system is not overclocked in any way?