*
If you have :
on F5 with default parameters works fine
only 12gb (10gb usable) and memory working on 1066
You have one memory stick bad , i have also a problem similar with 3 * 2 GB sticks with 6 GB detected and only 4 GB running
Only with one stick in the computer , the bad stick installed in slot one , and computer cannot start !!
You have 4 sticks why not test one by one and after two by two the sticks ...
Pierre