Are your polkaudio speakers powered? I mean, do they have a light on them that comes on when they are turned-on?
I've seen several types of speakers that are NOT powered- as in they just connect to the PC and do not have a power plug or ac adapter. If this is the case, this NON powered speakers are meant to plug into the HEADPHONES jack on the back of your computer, NOT the speaker jack.
If non-powered speakers are being used, be sure they are in the headphones jack. If in the speakers jack, they will do precisely as the poster has described- even fully cranked up in Windows and the speakers volume knob- they will just be very, very quiet. Moving the jack over to headphones should cure it.