Greetings,
Unplug your system
Ground yourself
Carefully remove and reseat each memory module
Retest
***Further steps
Remove memory and inspect slots for bent pins
Confirm full amount of memory is detected in BIOS
Use setup defaults - retest
If XMP capable, select this option - retest
Test with other memory
***Last resort, remove CPU and inspect socket for bent pins
Error means simply, no memory is detected when its expected.