Do socket 939 boards have problems with running memory at cas2? I have 4 sticks of Corsair CMX1024-3200C2 but I get bluescreens when I try to boot into windows at cas2, memory voltage is 2.75 and timings are 3-3-3-8 @ DDR400.
I know it's always best to have 2 sticks rather than 4 but I'm surprised it's only stable at 333mhz. Have you checked what timings are recommended for the memory @400mhz and the volts it's rated at? Check packaging or google for the info.