What kind of speakers do you have? If you're only using a 4.1 or 2.1 system that doesn't have a center/bass channel input, you won't be able to ajust your bass with the nForce control center. If you do have the correct speakers for the job, it's possible that you just have it set on the wrong speaker setup inside the control panel. It should be on 5.1 or digital, depending on your speakers.
Or if there's just the normal bass and treble sliders and those are faded, I have no idea.