I have this exact same problem, did you ever find a solution?
I have a Dell inspiron 1420 and I had to reinstall Vista on it, after the installation was complete I rebooted the computer and now the speakers won't work. The drivers are installed, and the computer recognizes both the drives and the speakers as working properly. I can see on the "sound meter system" that it is picking up sounds, but for some reason they just won't come out of the speakers.
I have tried, and tried again to reinstall the drivers, I've done everything that I can think of. Please, give me some help here.