Audio Systems: Car Audio, crossover settings, alpine stereo

Question
I was in my son's truck the other day and couldn't get the station I wanted and started pushing buttons on his alpine stereo.  The power seems to be working but there is no volumn.  I don't believe it has to do with the mute because my son has tried to get the volumn to work and he is very familiar with the stereo and he can't get it to work.  Any ideas??

Answer
there are crossover settings to change or turn off channels   to be used only if you install car amplifiers
but it is on the menu of the radio  there is also a mute but it lowers the volume 90%  
and there is source volume   try cd or am radio
good luck