Hi,

I posted an answer about solving Ubuntu sound problem in this post.

Have a look it might help you with you sound problem.

All the best.

I had the same issue - I had system sounds but video/movies and music apps would not play sound.

This resolved it for me. I use OSS (open sound system) This command lets you choose your default sound system, so therefore the apps within Ubuntu know what to use to play sounds. =]

goto a terimal and type

sudo dpkg-reconfigure linux-sound-base

Choose your sound system - By default for Ubuntu it is ALSA

G'luck