1-make sure the speakers are plugged in correctly and turned on
2-right click My Computer, click Properties, Hardware tab, Device Manager, make sure there isn't any red x's or yellow !'s by anything
3-open Start-Programs-Accessories-Entertainment-Volume Control, make sure nothing is muted or turned all the way down
4-in Volume Control still, click Options, check Advanced Controls, in the left column click the Advanced button, at the bottom of the window that pops up, check if Digital Output only (or similar) is checked, try alternating settings