Logitech X-530, 5 speakers on Dell Vostro1000

Hello,

I have Logitech X-530 5 Speakers and the sound isn't working on all speakers... i have a Dell Vostro 1000..
I have whatever was originally on the Laptop (Dell Vostro 1000.. Vista Basic) when it was made... so i have SigmaTel High Definition Audio CODEC. Do i need a sound card or something? If so which one? or what is the problem?? The sound only comes out of two speakers at a time...and they don't all work at the same time but the all do work though... if you have more questions just ask in your answer.