Likely your alsa default voume is not turned on.
Open a terminal window (KDE desktop- System- Konsole)
Now play with the settings until you get some sounds. To test you can use System Settings from KDE desktop main menu (K at bottom LH of screen), then Sound System, and Test Sound. Press Esc key to exit alsamixer. If you can't get a sound there is something else wrong.
sudo alsactl store
Now the system *should* pick up the stored defaults at reboot. It stores the file with the settings in