I'm having a major problem. I just bought another 2GB of Corsair TWIN2X2048-6400 (2 x 1GB). My computer does not want to run AT ALL with 4x1GB. It crashes all over the place, even when running the memory at default speed. If I take out 2GB, the other 2GB works fine just as it always has.

What can I do to run all 4GB at once?