Are you using the Dell supplied sound
driver or a driver from somewhere else? I used to do a lot of support on the Dell forum and we found in most cases the Dell sound driver was required. Non-Dell
drivers either did not work or did not work correctly.
You can download the Dell sound driver from
www.support.dell.com use your service tag number to access the downloads. If you would have provided the Vostro model number, I could have linked you directly to the correct download.