I have an Intel DX58SO motherboard and I recently acquired 3 sticks of 4 GB (http://www.newegg.ca/Product/Product.aspx?Item=N82E16820148789 http://www.newegg.ca/Product/Product.aspx?Item=N82E16820148789). The motherboard only recognizes 6 GB instead of 12 GB. I have the latest version of the BIOS and I've tweaked the memory settings a bit with no luck. It still only detects 6 GB.
How can I get my RAM to show up?
The supported memory clock speed for the processor is 1066 MHz but besides that I would ask Crucial* regarding the memory density as it may not be compatible (as you may need to use 2 Gb memory technology).
"DDR3 1600 or higher memory support on this motherboard requires compatible XMP enabled memory or advanced knowledge of BIOS and manual memory tuning. Individual results can vary."
http://www.intel.com/support/motherboards/desktop/dx58so/sb/CS-029865.htm Intel® Desktop Board DX58SO — System Memory