I have no volume going to my speakers,there's the static noise when stereo

[Tina Hall]

is turned on then nothing,why? Just recently my car stereo's has had no volume going to the speakers,everything is on and i can even hear the static connection to the speakers then nothing,even when i put a cd in there's no volume,ive had it back to the people who put the stereo i and they reckon they cant find anything wrong and that i may need a new stereo,can you help please.