No Sound

My OS is Ubuntu 12.04.
I've installed Musescore 1.2
At first install, I could hear the sample music and I then entered a small bit of music to check out the various sounds available and see how things worked. I was able to listen to what I wrote and edit what I wrote. Then the sound quit. I don't know why. I've tried uninstalling and reinstalling Musescore, to no avail. All other aspects of sound on my computer still work. I'm not sure where to look in order to troubleshoot the problem.