The latest firmware (bios) for that board is F4B released 2. Your description of the memory config implies that you have the banks crossed with one 4GB and one 2GB in each bank. This image is directly from the manual for that motherboard. Then verify they are in the proper slots per the mobo manual. While it may not be the cause, please remove the one potential issue and remove both 2GB modules so you are left with 2 4GB DIMMs. It is always recommended to have the same size memory modules installed.
