So I bought another 6GB Corsair Dominator DDR3 1600MHz kit and now I have a total of 12GB of ram (6 sticks 2GB each. 3 sticks on the BLACK memory slots, and 3 sticks on the BLUE memory slots). My mobo is ASUS P6X58D Premium. I also have Windows 7 Pro 64-bit. After installing the kit, I pressed the MEM RESET button on my mobo to reset the settings to get full 12GB. Did some research, and I found out that XMP mode will give me the full 1600MHz, at 1.66 DRAM Frequency. Now I never touched the DRAM settings the X.M.P mode did it all automatically just like it said in BIOS. I boot up and I see 12GB. Next day when I boot I only get 10GB. So I switched backed to AUTO for everything in BIOS instead of XMP profile for the mem sticks. After doing that and resetting the memory settings with the MEM RESET button again, it goes back to 12GB, then after than I STILL get 10GB. Its driving me off the damn wall and I dont know what else to do at this point. My system is NOT OCd im running on everything stock. Can someone PLEASE help me figure out this problem.
 
My specs are as follows (SIG)

would it matter if CPU Z says that I have 12288 MBytes and so does the BIOS?

Ok ill try that. So basically boot iwth 6GB (3 sticks) and if it shows 6GB then obviously they're ok, and if it shows 4 out of 6 then one stick is back and I can just call Corsair and have them ship me a replacement, or New Egg.

right. Thanks for the help. Ill see what happens