Could be problems with hardware issue. Do you have a spare set of speakers or a spare sound card to check to see if your speakers is the problem or not. If its not the speakers could be a defect in the sound card its self
^^ You shouldn't HAVE to; I used to run with my onboard, USB audio, ASUS Xonar D2, and Razer Barracuda all plugged in at the same time. [Granted, I could only use one at a time...]. The "Disable onboard sound" is a "Fix" unique for Creative.
Try Daniel_K drivers, and check control panel to make sure the right device is enabled.