Just tested a mp3 player in the Aux connector and the subwoofer receives audio. Bass sounds great; now it's just a matter of getting the PC to recognize it.
Well the problem here is that the sound card you have outputs high frequencies to the green channel because it thinks it's running in some sort of surround sound mode. Try changing the setting to something like "heaphones" and see if that works. Also, make sure your speakers are plugged into the GREEN port on your soundcard.
Try plugging the speakers into the heaphone jack on the front of your computer.