After upgrading to Linux Kernel 3.4, i noticed that there were no sound on my desktop and workstation. I think it was because of the new kernel and i used to have this problem as well in the past. The solution was to re-execute alsaconf to detect the sound card again. This time, this trick didn't work out. Strange thing is that mpg123 works on terminal/konsole.
Since amaroK is tied with KDE's backend, i tried to change the Phonon backend to Xine and VLC (i used MPlayer as the default), but didn't work as well. I tried GStreamer, but no luck as well. So i think there were some modules in GStreamer that i didn't install on my system. I fired up my browser to download the SlackBuilds and the source from the latest version of GStreamer and all of it's modules and compiled it. Unfortunately, the latest gst-plugins-* removed one module that are required by amaroK, so i had to stay at 0.10.x series for the time being. I re-downloaded the latest 0.10.x series and once everything has been upgraded, i recompiled amaroK 2.5.0.
When amaroK has been finished compiling, i switched to Phonon Gstreamer and now amaroK is able to play MP3 files again.