When I first installed Linux, I found that, even though I had downloaded the codecs for the media I was trying to play, that I had no sound.
I eventually found that the permissions on the files in the ALSA folder (sorry, I don't recall where that was) were wrong and that opening up the permissions on the folder allowed the system to use the files to play sounds.
I hope this helps!
P.S. Helpful sites for Linux audio are;