|How much can the motherboard/model support for ram in total?|
What is the largest single stick of ram that each module can support?
How large are the sticks that you have purchased?
How many slots are there, 4 I am assuming?
Is the ram seated in the modules properly? If you take out one of the new sticks will it boot? If you take all the new ram out does it then boot? Crucial.com has an analyzer that can answer most of those questions about what the board and module size supported are.