Problem with logitech x 350 spikers

Hello,

I have the Logitech x520 speakers and Windows vista . Since I've installed the new os, my 5.1 has not been working. Just the main front left and right speakers work, plus the sub
How come my speakers test correctly, but when I play music, only two +sub work?!?! Any fixes for this?

i have just Bought them plise help

i wan tell you it work good 5.1 all speakers with my DVD player


Thanks.