Having just purchased a Vostro 420, I purchased another Hard Drive, as I wished to triple boot and the supplied disk was to small for my requirements.
On installing Windows Vista B + W7 and Ubuntu 9.04 as a triple boot machine, everything worked fine on both flavours of Windows, But could not get the sound to work in Ubuntu, even tried a fresh install, but still no sound.
I had used the official Ubuntu 9.04 iso, as I knew what the partition structure would turn out like with this iso as I had used it many times before without any prob's rather than the Dell Ubuntu iso - which I had never used, so did not know what the result would be.
Knowing that there was not a problem with my machine, as everything worked OK under Windows, and that Ubuntu 9.04 worked perfectly on quite a number of other machines I have installed it on, it was obviously an incompatibility problem between the Vostro's HD sound hardware and Ubuntu.
I tried the Ubuntu forums (ncluding this one) to see what others had got similar problems and how they had resolved theirs, but having tried for a day and a half trying different suggestions, but nothing working.
Decided to give it one last shot, by googling (worldwide) to see if there had been anyone reporting problems similar to my own and BINGO the first post on the page was someone with the same machine as mine with exectly the same problem, Also the thread said that the problem had been SOLVED which realy made my day.
If anyone else has a sound problem due to a hardware conflict, then please read (all of it, as I remember seeing it on the Ubuntu forums):-
But the most important part of it is the remedy, which was here:-
For those not familiar with the command line - do as I did, which was write down the No.of tasks to do (9) and a b a etc for the No of items in each task, ticking each one as it is completed.
Open up the link above and also the Terminal (Applications/Accessories/terminal), then copy each line/command and past it to the last line in the terminal.
Do not get scared when there is much activity in the terminal, when you paste the command and then press enter, just make sure that everything stops and you are returned to the prompt before doing anything else.
I hope this helps someone else,as it helped me - what a relief to hear the sound as usual on the final restart.