|Also try each stick in each socket to make sure you do not have a bad socket.|
Make sure the memory is on the support list for your board.
Are both memory sticks the same specs?
Make sure you have 64bit version of Windows 7, 32bit does not support that much memory (it should just ignore it, but you never know).
Run Memtest86 on each stick of memory through a bootable CD to test them.
Post back more details.
You have to be a little bit crazy to keep you from going insane.