You have to set trfc to 52-62 for 2x2GB of ram, and you also are going to need to manually add soem MCH core Voltage. 1.1 I think is your default, so try 1.2 and or 1.3
If you still have issues Greg can likely tell you for sure if that ram has been tested in that board, Not so sure it has been but Mushkin makes great products that work superbly in P35 boards. >>>>
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Have you tested each stick in a different system or yours by itself with Memtest86+ to be sure you did not geta DOA stick? It happens >>>
http://www.memtest.org/#downiso