First, jaquith is "da' MAN!!!" on Tom's when it comes to memory config/issues. Listen to what he tells you and you'll likely find a workable solution.
Second, make sure your BIOS has the memory options set to default. You want no custom settings in place until you can stabilize the system. A simple reset of the BIOS (pull the battery method) should set you back to the original config if you can't select in the BIOS itself for some reason.