Question : Problem: Sound suddenly stopped working, both in Linux and in Windows

Sound suddenly stopped working.  Some details that are helpful to know:
Dell XPS 410 Desktop, 2 GB RAM, dual boots between Ubuntu Linux 7.10 and Windows Vista Business Edition.
Same day, for no apparent reason, sound stopped working on Linux desktop.  I checked all connections, removed the speaker jack from the KVM switch, plugged directly into onboard sound on back of computer - no joy.  Tried directly plugging into the back of the computer with headphones and another set of speakers.  No joy.

Verified that the onboard sound was still enabled in BIOS.  At this point, I assumed that the hardware connection in the back of the computer was bad.  I purchased a Soundblaster Audigy SE sound card after researching that it would work both with Vista and that there were Linux drivers available for it.  The card arrived today.  I installed it, verified that it was connected properly and restarted the computer.  I booted to Vista, since there was already a driver CD for it and installed the drivers.  

Still no sound.  I have verified that I see the sound devices in Hardware Mangler and they all say working properly.  The installation of drivers occurred without error or problems.  Again, I am testing with headphones and multiple sets of speakers but not receiving any sound.  I figured that the Windows plug-and-pray with a verified install program and tested drivers would resolve the problem but so far am unable to figure out why I am not getting any sound.  Even if the problem was the mobo and onboard sound I can't see why the card wouldn't work.

the machine is not causing me any other problems.  I've not seen any incidents or errors that would cause such a problem.  I had been playing music the night before and when I got up in the morning the sound was off, but it always is if the music files are finished and by morning they always are, and I didn't attempt to run any sound until later in the day when I discovered the problem.

Answer : Problem: Sound suddenly stopped working, both in Linux and in Windows

Now you should uninstall the previous drivers before installing the new ones. Start with Vista.