in kcontrol (configuration panel of kde), go to [sound and multimedia -> sound system] and check if you can test the sound over there.
If not, try to activate the sound system at that panel, or go to [sound and multimedia ->system notifications]
in the lower right corner, you see a button for player settings
open it, and select [use external player] and give a player command like play or aplay
you can check wich command works to play a file from the commandline, like
aplay /usr/share/sounds/sound.wav
Regards, Rinse