I recently bought logitech x-530 5.1 speakers. i hooked them up, and pluged it into my pc. Theres a problem though, when i play music, watch videos, or any kind of sound in general, sound only comes out of the front right and left speakers, and the bass. no sound comes out from the back left speaker, back right speaker and the centre speaker....whats wrong? this happens in all application like windows media player,vlc player,winamp etc.