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Well, not sure why that is, have you tried with just the new stick to make sure it is working correctly? If it is, you may have a bad board. Make certain you are putting the memory into the correct 2 slots, the Phenoms are picky about this. They don't really run in dual channel mode either, they use what is called "ganged" and "unganged". By default, with 2 sticks of memory, they run in the "unganged" mode. Phenoms have 2 memory controllers, and are actually faster this way. (if you have a Phenom processor)