SimplyLost

I just purchased a HP Pavillion with an AMD Phenom Triple Core Processor. I hooked up my Logitech Z-640 5.1 speaker system to the appropiate jacks, but no sound comes out. Realtek High Definition is the contoller. When I plug one of the wires from the Logitech system to the "out" jack for the monitor, the speakers connected to that wire work, but not from the "front, rear, or cent/sub" jacks. Please help.