Solution: on MB: Asus P7P55D-ELX
Turned out to be a memory/Bios Setting issue:
8GB(4x2GB)installed, Bios and Win7_64 shows only 4GB, 4GB hardware reserved
Finally got it to work with 8GB:
What I did:
Clear CMOS: Short CLRT pins on MB, short pin2,3:, (Not just reload defaults in BIOS), and back to Normal: short Pin1,2
Press MemOK, a Asus MB feature that sets Memory timing parameters automatically
Delete, to get into BIOS:
Now BIOS/Main/System Info: Usable Size: 8191MB (and Win7_64 reports 8GB)
Note: unless Bios shows correct size, Windows wont see it.(even though CPU-Z will report it).
I had tried all else without luck. Key was to hardware clear CMOS on MB.