After you install the PCLOS iso (that was released in February), next you have to do is to update your system. The update will bring a new KDE base, and besides this, the sound will disappear :)
No sound on PCLOS 2012-2
Luckily this is easy to fix - open terminal, become root and run:
Agree with what alsaconf says, let it detect your sound card once again. In the end it will congratulate you that your sound card has been detected and that you now have sound on your system.
Basically, this works for any linux system. If you for example have no sound on Ubuntu, you can similarly run: