which cabinet are you using? does it have front audio port? if yes, did you tried plugging in your speakers there?
uninstall the audio drivers & reinstall Win7 (update it). this will install the generic windows audio driver. you can check if the generic audio drivers are in use after you uninstall the current drivers by using this software & navigating to the audio tab:
Speccy.
you can also try using any mobile 3.5mm headset to test the system, maybe your speaker is faulty.