Upgrading DDR Ram problem from 2x to 4x

[Malink]

I currently have 2x 512 MB pc3200 non-ecc unbuffered from crucial installed on my computer. I bought 2 more sticks that were exactly the same kind and tried installing them on my computer. My computer turns on but it doesn't boot up. The power is on as well as all the fans and the LED's but nothing comes on the screen. When I remove the new Ram it boots up fine. Then I mixed and matched every stick in different combinations and discovered it only works when I put 2 sticks of ram (regardless of the which stick is in) in the correct dual channel combination. All the sticks work too because they all work when they're in this configuration. What could be the problem? thx

I have an asus A8N-SLI Delux Mobo, 2x asus 6800 gt (SLI), p160 antec case, antec 480 neopower, amd 3500+ (san diego) 939, 2x 512 MB PC3200 non-ecc unbuffered ram, audigy platinum soundcard