Here is the Maintenance and Service Guide for the computer. Beginning on Page 90 you will find the System Board Connections. Then, beginning on Page 91-94 you will find the information on the memory. There is a detailed explanation on how you should populate the DIMM Sockets. Read all of this information carefully and it should help you solve your problem.
Also, here is the memory recommended by Crucial Memory. Their Ballistix Sport memory is very fast. If Crucial recommends the memory it will be replaced at no additional cost to you if it doesn't work. Their Tech Support will help assure that works properly.
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